Abstract: Concentrated on the mis-matched welded joints containing crack on the fusion line, plastic zone and compound angle were analyzed by using elasto-plastic finite element method.The relationship of plastic zone, strength matching and compound angle of welded joints containing single-edge crack on the fusion line was studied.The results show that strength matching has an obvious influence on the plastic zone for welded joints with crack on fusion line, i.e., plastic zone preferentially make development for material which has less yield strength, and plastic zone of under-matched welded joint is larger than that of over-matched welded joint in the same load lever;the crack tip field plastic zone decreases with compound angle, that is to say, when load lever is lower than yield strength of both sides of materials in interface crack, their relationship is linear, otherwise, their relationship is non-linear in welded joints.