Temperature field and thermal-structure coupling stress field calculation were conducted to a main steam safety valve prototype for nuclear power stations using finite element software Ansys,and the stress of the valve subjected to operating pressure load and thermal stress was in compliance with the stress evaluation criteria. In addition,alternating stress of the pressure components for the specified cyclic operation application of loads and thermal stresses were calculated,and fatigue analysis was evaluated according to RCC-M code. Results indicate that the valve prototype is able to meet the requirements of fatigue failure criteria for the specified cycles and would have good prospects in engineering applications.