Abstract: To deeply research the bending properties and design method of glass fiber reinforce plastic (GFRP) reinforced concrete beams, the flexural capacities of 36 concrete beams was investigated under the loading mode of four-point bending moment, including 21 GFRP reinforced concrete beams and 15 steel reinforced concrete beams. The deflection and flexural capacity were analyzed comparatively between the GFRP and steel reinforced concrete beams with the same parameters, such as reinforcement ratio, geometry size and concrete strength. The calculation formulas for the flexural capacities of the GFRP reinforced concrete beams and the critical relative depths of their compression zones were derived. The correctnesses of the formulas were proved with the test data. The research result shows that the ratio of the ultimate deflections of the two types of concrete beams is 1.5 to 2.5, the ratio of initial cracking load is 0.53 to 0.69, and the ratio of ultimate load is 0.75 to 1.02. In addition, the critical relative depth of the compression zone is from 0.17 to 0.20. It is suggested that reinforcement ratio should be equal to 1.4 times of balanced reinforcement ratio to improve safety storage.