Landslides, dust storms, sediment transport and ice transport in rivers, are all examples of granular flows that influence the environment. Physical experiments and numerical simulations designed to solve granular flow problems are limited to small sizes. To expand the computational power in order to simulate large systems of granular materials, parallel computing is necessary. In this paper we will present the results that compare single processor and multiple processor simulation results. We study one of the simplest granular flow geometry: a 2-D direct shear box. To benchmark the difference between a single and a multiple processor simulation, we use at least 60,000 particles in a shear box, comparing with 600 particles in the physical experiment. We adopt the OpenMP and message-passing interface (MPI) approach. A comparison will be made with 1 and 10 processors. The efficiency of using multiple processors will be discussed. The difference of the internal friction and the flow properties observed in different sample sizes will also be presented.