This paper studies the method of surface strengthening to 45 steel by laser-guided micro discharge, and compared the method by laser-guided discharge (LGD) with the method by high voltage-guided discharge(HVGD). It was found that the break voltage of electrode gap was decreased a grade, and the discharge pit was completely lapped over the laser focus by laser-guiding. The expanding speed of discharge pit was almost same in two kinds of discharge processing. Because of the effect of the diameter of initial discharge pit, the diameter of laser-guided discharge pit was always bigger than the diameter of high voltage-guided discharge pit. The most thickness of layer-strengthened in two kinds of discharge processing were almost same about 180 μm. The strengthened layer of discharge pit included the melted layer and hardening layer. The most hardness of strengthened layer was about 800 HV.