The mechanical properties of glass fiber reinforced polymer reinforcing bars(rebar) in various environment conditions such as moisture, chloride, alkali and freeze-thaw actions at temperature ranging from room temperature($25^{circ}C$) to high temperature of up to $80^{circ}C$ have been studied. The test results indicated that tensile strength and interfacial shear strength of GFRP bar were decreased with the increasing of temperature and holding time of each environment condition. The degradation in alkali environment. was more serious than those in the other environments.