A design method of beam splitter is proposed on the basis of the particular properties of surface plasmon polarizations in metallic nanoslits. The nanoslits with different width and depth can lead to different phase retardations while the surface plasmons passing through the structure. We can achieve a beam splitting effect with the splitting angle of near 90 by adjusting the width and depth of the slits accordingly. The numerical simulations using two dimensional finite-difference and time-domain (FDTD) algorithm is presented here to analyze working performance of the designed structure. Our computational results demonstrate that the splitting effect of the beam can be realized successfully.