In nuclear power pressure vessels, dissimilar metal welded joints (DMWJs) are the weak link owing to their highly heterogeneous microstructure, mechanical, thermal, and fracture properties; and some defects that occur at different positions within the DMWJs. To ensure the safety of nuclear power pressure vessels, it is important to examine the fracture behavior of DMWJ in detail. In addition to residual stress, constraint is an important factor affecting the fracture behavior of DMWJ. To understand this behavior, both constraint and residual stress must be considered. In this work, taking nuclear safety and DMWJ as the research objects, three-point bending (SENB) specimens with a central crack were selected. Different loads were applied to different sides of the specimen to produce different stresses at the crack tip, such as left and right, up and down, front and back, and both six sides, and the stresses were introduced into the SENB specimen as the residual stress by restart method. The fracture behavior of DMWJ was then systematically studied under various constraints considering residual stresses and the interaction between residual stress and constraint. The results showed that the change in residual stress significantly influenced the fracture behavior of DMWJ under different constraints. In contrast to the DMWJ with low constraint, the J-R curve of the DMWJ with high constraint was more sensitive to the change in residual stress. The main cause was the Mises stress at the crack tip and the triaxial stress. The direction of residual stress also influenced the J-R curve.