A YAG pulsed laser welding system was used to analyze the microstructure of welded 1Cr17Ni2 stainless steel plates, tensile properties and microhardness of the joints, and effects of different defocusing distances on the microstructure and properties of the welded 1Cr17Ni2 stainless steel plates. The results show that the laser self-melting butt welding in the 1Cr17Ni2 stainless steel plate weld shows a microstructure division. The main structure of the base material area comprises ferrite and martensite, the heat-affected area comprises lath martensite and a small amount of banded ferrite, and the weld area comprises mainly martensite. Weld penetration gradually decreases with increasing defocusing distance. Further, the weld width increases and subsequently decreases, the martensite content at the weld gradually decreases, and the joint's tensile strength increases and subsequently decreases. The joint hardness in descending order is weld zone > heat affected zone > base material zone. Thus, the joint's overall hardness decreases with increasing defocusing distance. When the defocusing distance is -5.5 mm, the martensite beam group in the heat affected zone is fine and even, the welding forming quality is good, and the joint has excellent tensile performance.