Abstract: By using a special two dimensional simple shear test apparatus with rigid lateral platens, simple shear tests are carried out on an assembly of aluminum rods, one of which is then simulated by distinct element method (DEM). The simulation results by DEM agree well with the test results. Based on the simulation results, the shear mechanism of granular materials in simple shear test, such as the frequency distribution and the variation of contact angles of particles along the mobilized plane, is studied.