Abstract: The steam generator is the key equipment of nuclear power plant. The stability and safety of the whole nuclear power plant will be affected by the leakage of steam generator during the normal work. The tube and tube sheet are connected by hydraulic expansion in steam generator. This expansion joint is the location liable to leak. It’s of vital importance to study the hydraulic expansion of steam generator. According to expansion test and pulling out force test, the reasonable pressure holding time was determined. On the basis of the finite element analysis, the residual contact pressures of different thick tube sheets were researched. The theoretical calculation formula of pulling out force was also presented. The results show that pressure holding time should be controlled in 6-8 s and the pulling out force in steam generator could be calculated with revised formula.