In this paper, numerical simulation for hydraulic expanding connection of tube to tubesheet was performed. Residual contact preesure on the contact surface between tube and tubesheet as well as residual expansion stress in the tubesheet were investigated. It is seen the distribution of residual contact pressure is not uniform. Instead, near the two tubesheet surfaces, there are two tightness bands on which the residual contact pressure is high. Based on the fact that residual expansion stress could be a driving force for the tubesheet cracking, it is suggested that the expansion pressure should not be too large but enough to completely form the tightness bands on the contact surface. With this criterion, expansion pressures for typical tube materals and size are given.