The load cases of ram air turbine （RAT） system are firstly analyzed aim at the storage scenario and utilization scenario. Then the mathematical models of the constraints under all the load cases are constructed. Based on these mathematical models， the structure optimization model of the ram air turbine system is established by using collaborative optimization method. In this optimization model， the multi-load-cases structure optimization is firstly carried out for the storage scenario and utilization scenario. Meanwhile， the optimized parameters are coordinated with aid of the dynamic relaxation factor. Finally， the integration of relative simulation analysis tools and the optimization are achieved in Isight multidisciplinary design optimization software. The optimization results show that the collaborative optimization method established in this paper can significantly reduce the weight of the ram air turbine system structures.