Objective: The fiber laser was used to weld 304 stainless steel and copper dissimilar materials to improve tensile strength of welds. The welding mechanism was analysed. Methods: The tensile strength of stainless steel/copper welds under different positions of laser beam was tested .The microstructure of the weld was observed by optical microscope, and the elements in the welds were analyzed by energy spectrum analyzer (EDS). Results: The experimental results showed that the maximum tensile strength of welds is 186 MPa when the laser beam is 0.15 mm close to the stainless steel side. Conclusion: The laser beam absorption rate on stainless steel is higher than that copper. The laser beam near the stainless steel side makes the stainless steel melt first, and then the heat conduction affect on copper to form a molten pool, and the stainless steel penetrates into the copper side to form a dissimilar metal welds.