Nuclear Steam Generators is very important equipment in nuclear reactor. It should insure sufficient cooling of nuclear reactor and prevent the damage of turbine blades. This paper proposes a new control strategy for Nuclear Steam Generators to ensure its safety and normal operating. The control method is based on fuzzy-PID and water mass inventory. In order to study the controller and validate & verify the control method, the paper adopt to full-scope simulator of nuclear power plants which can simulate the total plant operating characteristics. The simulation test results show that the new controller is superior to the conventional PID controller in controlling the Nuclear Steam Generators.