Abstract: In this paper,1. 2 mm dual-phase steel with different martensite content was welded with intermediate frequency inverter spot welder and welding process window was established,the influence of martensite content on welding process window was analyzed. The microstructure and microhardness of nugget were researched by OM,TEM and Vickers hardness tester. The results show that with the increase of the martensite content the welding process window is offset in the direction of current reduction,and Imin decreases by a small amount with the increase of martensite content,however Imax decreases a lot. The microstructure of the nugget is totally martensite. The microstructure changes from lath martensite to lath martensite plus twinned martensite with the increase of martensite content,Hardness in HAZ area gradually shows softening characteristics.