A parallel algorithm suitable for simulating multi-sized particle systems and multiphase fluid systems is proposed based on macro-scale pseudo-particle modeling (MaPPM). The algorithm employs space-decomposition of the computational load among the processing elements (PEs) and multi-level cell-subdivision technique for particle indexing. In this algorithm, a 2D gas-solid system is simulated with the temporal variations of drags on solids, inter-phase slip velocities and solids concentration elaborately monitored. Analysis of the results shows that the algorithm is of good parallel efficiency and scalability, demonstrating the unique advantage of MaPPM in simulating complex flows.