The work aims to improve the surface hardness of AISI304 stainless steel plate. Surface hardening treatment was carried out on 3 mm thick AISI304 stainless steel plate by explosive surface hardening technique. The microhardness and the microstructures of the cross sections at the different locations in the treated samples were measured and characterized by HXD-1000YM Micro-hardness tester and JEM-2010 transmission electron microscopy. Numerical simulation was carried out on process of explosive surface hardening by finite element software ANSYS/LS-DYNA. The average pressure and velocity of im-pact surface were calculated. The effect of the impact pressure and velocity on surface microhardness of treated samples at the specific points was analyzed by comparison of the numerical simulation results and the experiment results. From the numerical results, the average pressure at impact point was approximately 5.5 GPa and the average velocity at impact point reached 178 m/s. Error between the theoretical calculation and the numerical calculation of pressure and velocity on impact surface was less than 5%. Experimental results agreed with the numerical simulation results. The impact pressure and velocity near initiation and detonation ends after explosive hardening were less than that at the stage of stabilization detonations. Therefore, microhardness in the former is less than that in the latter. Distribution of hardness on the cross sections indicated that the microhardness of the impact surface was larger than that of the explosive surface and increased from 210HV to 450HV and the microhardness on the explosive surface increased from 210HV to 390HV. There exists the boundary effect in the explosive hardening process. Explosive impact treatment can enhance the surface hardness and entire hardness of plate remarkably. Improvement of surface hardness is related to formation of deformation bands and planar dislocation arrays.