Gas-particle two-phase mixing layer is simulated by a two-way vortex method to investigate the effects of the mass loading ratio and the particle diameter on the flow. The method, proposed by the authors in a prior paper, simultaneously calculates the behavior of the vortex elements, discretizing the gas flow field, and the particle motion by the Lagrangian approach, The loaded particle delays the pairing process of the vortex element. When the mass loading ratio m is increased, the pairing process becomes less apparent and the flow structures are elongated in the streamwise direction. With an increment in m, the gas velocity gradient in the cross-stream section becomes gentler and the center of the mixing layer shifts toward the low-speed side. The velocity fluctuation of the gas lessens at the center of the mixing layer and heightens at the edges of the layer due to the loaded particles. These chances are unremarkable when large particles are loaded.