Laser deep penetration welding (LDW) was used to weld T2 copper and SUS304 stainless steel. The effect of beam offset controlled by PLC on Microstructure and tensile properties of welded joint was studied. The results show that the profile morphology of T2 copper-SUS304 stainless steel welded joints with different beam offsets are straight on the copper side and hourglass on the steel side; the weld seam is narrower when the beam offset is positive and wider when the beam offset is negative. The results show that the width of the heat affected zone on the copper side is significantly larger than that on the steel side when the beam is positive offset (the beam is biased to the steel side), and the cellular dendrites near the fusion line are smaller and there are more granular Cu2O phases near the fusion line. When the beam is negatively offset, there are slender columnar crystals growing perpendicular to the weld seam and reticular cells near the weld center, and granular Cu2O can be seen locally Phase. The fracture position of welded joint with beam offset of 0 mm and +0.15 mm is at the weld joint, and the fracture position of welded joint with beam offset of +0.30 mm, -0.15 mm and -0.30 is in the heat affected zone of copper side. When the beam offset is + 0.30 mm, better welding effect can be obtained. The observation results of tensile fracture morphology of welded joint are consistent with the tensile test results.