In order to study the flexural properties of the fast-growing poplar glued timber beams reinforced by carbon fiber, the influence of factors was considered，such as different fiber distribution ratios and different fiber distribution positions. A four-point bending static load test of the beam was carried out, and the theoretical calculation formula of the ultimate bending moment of the beam was deduced. The results show that, compared with the pure glulam beam, the number and width of cracks of reinforced specimens decrease, and the elastic modulus, ultimate bearing capacity and initial bending stiffness increase significantly. The elastic modulus of the beam reinforced by carbon fiber increased by 28.02%~57.93%; the ultimate load increased by 16.47%~50.72%; the initial bending stiffness of poplar beam increased by 11.58%~23.37%. The ultimate bearing capacity and initial bending stiffness of beams with carbon fiber in tension zone can be effectively improved. Compared with the specimen only with carbon fiber in the tensile zone, the load-bearing capacity of the specimen is reduced when the carbon fiber is added in the tensile zone and the compression zone, but the deflection in failure is reduced. The fiber distribution rate in the tensile zone of the specimen should be between 0.060 6% and 1.031 1%, which can give full play to the plastic compressive properties of wood. The bending calculation formula of the beam was obtained. The calculation results of the ultimate bending moment of the specimen are consistent with the test results, and the calculation results can predict the ultimate bending moment of this kind of specimen under bending.