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 test of the beam was carried out. The results show that, with the increase of carbon fiber content, 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 is increased by 28.02%~57.93% compared with the pure glulam beam; the ultimate load increased by 16.47%~50.72%; the initial bending stiffness of poplar beam increased by 11.58%~23.37%. The capacity and stiffness of beams with carbon fiber in tension zone can be effectively improved. The load-bearing capacity of the specimen is reduced, but the deflection is reduced when the upper part is equipped with carbon fiber. The fiber distribution rate in the tensile zone of the test piece should be between 0.0606% and 1.0311%, which can give full play to the plastic compressive properties of wood. The calculation formula of the beam was obtained. The calculation results of the specimen are consistent with the test results, and the calculation results can predict the ultimate bending moment of this kind of specimen.