To investigate the influence of alkali environment on the mechanical performance of reinforced concrete (RC) beams strengthened with GFRP sheets, monotonic static tests were conducted on GFRP sheets and RC beams strengthened with GFRP sheets respectively.Which had been subjected tothe corrosion of alkal:solution Experimental results show that mechanical performance of GFRP sheets degenerates significantly in alkali environment, while the impregnating resin can obviously improve the durability of GFRP sheets. Degeneration of the bearing capacity and deformation performance of the strengthened beams is not apparent after being soaked in the alkali solution with pH 12.8 for 60 days. Mechanical performance of the strengthened beams is closely related to the interface adhesive property between GFRP sheets and RC beams.