With the continuously development of civil aircraft, the ratio of composite used is growing higher and hybrid connection between composite and metal is growing. The range of environment temperature is large and varies from -75 ℃ to 55 ℃, it is necessary to study the thermal strain of composite and stress of metal hybrid connection structure. Control variable and comparison methods were used to study thermal stress of different titanium alloy and aluminum alloy thicknesses connected with the same composite by FEM computation. Results show that for the same composite structure and specific metal thickness range between 3 mm and 6 mm, composite thermal strain decreases when the thickness of titanium alloy increases and it is more sensitive to the thickness of titanium alloy compared with the titanium alloy itself, which also increases when aluminum alloy thickness increases for the same temperature. Thermal stress of titanium alloy decreases when its thickness increases while aluminum alloy decreases when its thickness increases. The research results have certain kinds of meaning and value for reference.