Abstract: Through reasonable simplification and equivalence finish, a detailed nonlinear finite element model of steam generator (SG) of a domestic 3rd generation nuclear power plant (NPP) is established. This model is then connected with the reactor coolant loop (RCL) to carry out the analysis of dynamic response for SG LOCA shaking. By calculation, the maximum absolute stresses of SG heat transfer tube bundles and its variation with tube diameter and reacting forces of upper supports are obtained. In order to study the effect of SG decoupling from the RCL on the shaking dynamic response, a comparative study of decoupling /coupling methods is developed. Results show that SG decoupling has a significant impact on the calculation result, and the calculation method of coupling is more closer to the real situation and should be recommended.