In order to meet the requirements of environmental temperature, complete quickly and reliably the design scheme of FOG combination, the thermal design and analysis of FOG combination were carried out. The combination model and finite element model were established, the boundary conditions and constraints conditions were set, the temperature and the reliability of the key components and assemblies of the combination FOG were analyzed in entire temperature cycles. Finally, the maximum temperature of DSP was reduced by 10 ℃, the maximum temperature of DC/DC power modules was from the original 90 ℃ down to 70 ℃, the all critical components and assemblies were working within their rated temperature range through the way of thermal design, the uniformity of fiber optic gyroscope combination of internal temperature field was improved, from the original 30 ℃ down to 10 ℃, a basis was provided to determine the design of scheme.