Abstract: To deeply study the shear behavior of concrete beams reinforced with glass fiber reinforce plastic (GFRP), factors influencing the shear capacity of a GFRP-reinforced concrete beam were investigated through tests of 57 concrete beams. The investigation mainly concerns the influences of stirrup and shear-span ratio on the shear capacity. In addition, a comparative analysis of concrete beams reinforced respectively with GFRP and steel on the shear capacity was carried out under the same parameters, such as reinforcement ratio, geometry size, concrete strength and shear-span ratio. The relationship between the influence coefficient of GFRP on concrete shear capacity and the shear-span ratio was researched. The results show that stirrups make the initial cracking shear strength of a GFRP-reinforced concrete beam increase about 7.4% to 30.0%, and the maximum stirrup stress is much less than its tensile strength when the concrete beam reaches its ultimate load-bearing capacity to indicate that the effective strain of stirrup controls its shear strength. The shear capacity of a GFRP-reinforced concrete beam increases firstly with the reduction of shear-span ratio, and then decreases. The influence coefficient of GFRP on concrete shear capacity increases with shear-span ratio reducing.