Abstract: The flexural properties of cement mortar externally bonded carbon fiber sheets under different moisture and heat environment were studied by means of three-point bending test.The fracture modes of CFRP-cement mortar system were examined.The experimental results show that when the specimens were immersed in 25 ℃ water for 1 to 5 days,their strength did not change with the time.When the specimens were immersed in 60 ℃ water for 1 to 5 days,their strength increased with the time.When the specimens were immersed in 90 ℃ water for 1 to 5 days,their strength increased for 1 to 3 days,but decreased for more than 3 days.The fracture modes of CFRP-cement mortar specimen were accumulation with certain ductility,when they were immersed in 25 ℃ and 60 ℃ water for 1 to 5 days,as well as 1 to 3 days at 90 ℃.But when they were immersed in 90 ℃ water for 5 days,the brittle collapse took place.