Objectives: When the gasoline engine works at low speed and low load, the introduction of homogeneous EGR (exhaust gas recirculation) can reduce the engine pumping loss and NOx emission, but a high homogeneous EGR ratio will deteriorate the combustion. In order to improve the tolerance of the engine to EGR, the EGR stratification technology can be used; at the same time, due to the low intake air flow velocity and the in-cylinder airflow cannot be effectively organized, the turbulent kinetic energy in the cylinder at the ignition time is low, resulting in slow combustion speed and low thermal efficiency. So as to improve this situation, it is necessary to increase the intake air flow velocity and make the in-cylinder air flow well organized. Therefore, this paper transforms the intake bypass system of a motorcycle gasoline engine into an EGR system, in order to achieve EGR stratification and improve the in-cylinder overall flow characteristic parameters at the ignition time. Methods: Using a combination of theoretical derivation, 1-D thermodynamic numerical model, and 3-D in-cylinder flow simulation, the 1-D GT-POWER calculation model of the engine with EGR and the 3-D CONVERGE calculation model of the engine's first cylinder were built in turn. According to the design parameters of the exhaust gas incident pipe: installation angle θ, installation distance δ, and pipe diameter d, 8 comparison schemes are set up. Use GT-POWER to solve the initial conditions and boundary conditions of each scheme, and import these conditions into the CONVERGE model of each scheme for solving; the influence of pipe parameters on the in-cylinder flow is measured by the in-cylinder overall flow characteristic parameters, and the influence on EGR stratification is measured by the in-cylinder exhaust gas mass fraction nephogram and the velocity field nephogram; the optimal parameters are determined according to the EGR stratification effect and the in-cylinder overall flow characteristic parameters. Results: ①The high-speed exhaust gas jet makes the in-cylinder turbulent kinetic energy of each EGR scheme much higher than that of the original machine. When θ ≥ 17.5°, the maximum turbulent kinetic energy can reach 67 m2/s2, which is 3.4 times that of the original machine. Near the ignition time, thanks to the crushing of the tumble flow in the later stage of compression, the attenuation of turbulent kinetic energy is delayed, resulting in a significantly higher turbulent kinetic energy of the EGR scheme than the original engine, and the minimum turbulent kinetic energy of each scheme can still reach 18 18 m2/s2 (θ = 11° ), which is 2.3 times that of the original engine. At the same time, under the action of high-speed exhaust gas jet, the in-cylinder airflow is effectively organized, the maximum swirl ratio at the intake bottom dead center is 3.4, and the minimum swirl ratio at ignition time is 2.2 (θ = 11°). However, the tumble ratio and swirl ratio of the original engine in the entire intake stage are basically 0. ②Regardless of whether the installation angle θ is too large or too small, the interference of the exhaust jet will be enhanced, resulting in an increase in energy loss, which is not conducive to improving the turbulent kinetic energy at the time of ignition. When the installation angle is relatively moderate, such as θ=17.5°, the turbulent kinetic energy at ignition time is 27.4 m2/s2, which are higher than those of θ=11°(18.3 m2/s2), θ=15°(24.4 m2/s2), θ=19°(17.0 m2/s2) scheme. Reducing the installation distance δ will significantly reduce the swirl ratio while increasing the turbulent kinetic energy. At ignition time, the maximum turbulent kinetic energy at δ=7 mm is 36.2% higher than that at δ=22 mm, but the maximum swirl ratio at δ=22 mm is 4.9 times that when δ=7 mm. The larger the pipe diameter d, the larger the turbulent kinetic energy, swirl ratio and tumble ratio at the ignition time. Near the ignition time, the turbulent kinetic energy of d=5 mm is 1.8 times that of d=3 mm. ③Compared with the in-cylinder velocity field, from the start of intake to the ignition time, both schemes 7 and 8 can form radial velocity stratification, and the overall velocity is higher than other schemes. Comparing the in-cylinder exhaust gas mass fraction distribution, schemes 6, 7 and 8 can all achieve EGR stratification at the ignition time. The high EGR ratio area is mainly concentrated in the central area of the cylinder, and the low EGR ratio area is mainly distributed near the spark plug and the top of the combustion chamber. The difference between the two EGR ratio is about 10%. Conclusions: Combined with the influence of the parameters of the exhaust gas incident pipe on the EGR stratification and the in-cylinder overall flow characteristic parameters and the actual processing feasibility of the pipeline, scheme 7 (θ=17.5°, δ=22 mm, d=5 mm) is selected as the optimal scheme. This scheme can improve the in-cylinder overall flow characteristic parameters at the ignition time while realizing the EGR stratification in the cylinder.