Most parts of south China are located in subtropical region，where hygrothermal environment will reduce the performance of prestressed CFＲP reinforced ＲC structure． In order to explore the influence of hygrothermal environment on the fatigue performance of prestressed CFＲP reinforced ＲC structure，the failure criterions were established in the paper based on the two failure modes of main reinforcement fracture and debonding failure of CFＲPconcrete interface under the combined action of hygrothermal environment and fatigue load and the fatigue performance of prestressed CFＲP reinforced ＲC beams in hygrothermal environment was analyzed by numerical analysis． The results show that the fatigue performance of the reinforced beams will be reduced in hygrothermal environment， and the effect of increasing the prestress degree of CFＲP on the predicted life of the beams presents two circumstances． When the ＲC beams are damaged due to the failure of the main reinforcement，the increase of prestress degree can significantly increase the predicted life of the ＲC beams． However，when the beam is damaged due to the interface debonding，excessive prestress will reduce the life expectancy of ＲC beams．