In this article, ten kinds of granular materials with different particle gradation curves based on the regularized incomplete Beta function are produced and packed by discrete element method. Then the influences of particle gradation on granular packing and frictional characteristics are examined. Merely adjusting the two parameters in the regularized incomplete Beta function, we are able to generate a numerical granular material with all kinds of granular packing, either well or poorly graded now. The model is proved to be a very useful tool for conventional discrete element method to simulate mechanical behavior of realistic granular materials.