The invention relates to the technical field of laser machining, in particular to a gradient transition connection method of steel/titanium dissimilar metal based on laser synchronous preheating deposition. The method comprises the following steps of (1) machining and cleaning a substrate, wherein the joint form is butt joint or corner joint; (2) preheating, specifically, preheating the cross section of the deposition position of a titanium alloy base material by adopting laser; (3) powder preparation, specifically, weighing the stainless steel and the titanium alloy, and separately mixing theweighed stainless steel and titanium alloy with a nickel-based alloy; (4) laser deposition and synchronous preheating, specifically, preheating a deposition layer after laser deposition for a certainperiod of time, then continuously depositing, and alternately performing; (5) post-heating, specifically, continuously running the laser to perform post-heat treatment on the deposition layer; and (6) welding, specifically, obtaining the titanium/nickel/steel gradient deposition layer and performing welding. The method solves the problems of low strength and poor toughness of a welding joint caused by the fact that a continuous and high-brittleness intermetallic compound is extremely easy to form at an interface in the traditional fusion welding, high-energy beam welding and solid-phase connection process of the titanium alloy and the stainless steel at present.