Loss of coolant accident (LOCA) is one of most severe accidents of nuclear power plant. The coolant will discharge from the break when this accident occurs, consequently exert large hydrodynamic load on the primary loop system because of the fluid acting force as well as the propagation of pressure wave, then may further influence the pressure boundary of the primary loop. Steam generator (SG) is a crucial device with complex structure, hydrodynamic forces of its U-type tube and plate have been analyzed under various cases in this paper. Firstly, the reactor core and primary loop system of pressurized water reactor nuclear power plant (NPP) was modeled with RELAP5. Then a LOCA was simulated and the thermal hydraulic characteristics such as the pressure and mass flow rate were obtained. Finally, the forces at key positions of SG were calculated with the control volume integral method. The sensitivity analysis was also performed, including the break opening time, number of control volumes as well as the time step chosen in the hydrodynamic force calculation. The results have shown that the break opening time has a great influence on the numerical calculation that should be carefully set before the simulation, and the maximum hydrodynamic force is obtained under the condition that double-ended offset shear break at outlet nozzle of SG, and the pressure difference between the two sides of SG divider plate obviously increases compared with the normal operation condition. Thus, some meaningful suggestions have been provided for the design and safety analysis of SG.