Distinct element method is employed to simulate packing of spherical particles with different size distributions: equal-size, bimodal, and Gaussian. During the packing process, particles collide with their neighbors and bounce back and forth. Since the collision is inelastic, dissipative force exits, leading to energy loss in every collision. The interparticle contact force is calculated based on the nonlinear Hertz theory. The packing structures quantified by porosity and the coordination number under different particle size distributions are discussed.