OpenMP has been shown to be more efficient in performing coupled CFD-DEM calculations in parallel framework as compared to MPI by Amritkar et al. Recently, a multi-scale parallel strategy is developed. Generally, the simulation domain is divided into many sub-domains and each process calculates only one sub-domain using MPI passing boundary information; for each sub-domain, the CPUs are used to solve the fluid phase while the general purpose GPUs are used to solve the movement of particles. However, in this computation method CPUs and GPUs work in serial. That is, the CPUs are idle while the GPUs are calculating the solid particles, and the GPUs are idle when the CPUs are calculating the fluid phase. To further accelerate the computation, the CPU and GPU computing can be overlapped using the shared memory of a Linux system. Thus, the fluid phase and particles can be calculated at the same time.