Bonded T300/CYD128 composite repair of 1.76mm aluminum substrates was prepared by vacuum bagging technology.The hygrothermal properties of bonded composite repair of aluminum substrates were investigated,so do the composite material's pulling sample and it is epoxy casting sample.The Results show that the saturated water absorption of epoxy casting samples is 0.9%,but there is an obvious step in the water absorption dynamics curve.Along with the extending of the hygrothermal effect,the properties of composite material and its epoxy casting sample are increased at first and then decreased.The peak properties appear at 300 h(1 531 MPa) and 500 h(73.9 MPa) respectively.Along with the extending of the hygrothermal effect,the properties of cracking-aluminum substrates fall nearly linearly,the falling rate of fracture load is 0.12 kN/100 h.The properties of bonded-aluminum substrates are unstable.