A metallic grating structure which can enhance Second-harmonic Generation (SHG) based on exciting Surface Plasmons (SP) is studied. By designing the structure parameters of the metallic grating with quasi phase matching condition, the SP of the fundamental mode and the second-harmonic mode can be excited simultaneously, which considerably enhance the efficiency of SHG emission. Numerical simulation for SHG behaviors of designed structures were performed by using the Finite Difference-time Domain Method (FDTD) and the results showed that the quasi-phase-match condition and the excited SP mode made a key role for enhancing the efficiency of SHG. Moreover, the effect of the structure parameters of the metallic grating on SHG emission was analyzed.