With an aim to study gas flow information at a single particle scale, a Lagrangian method for gas/solid flow, termed pseudo-particle model (PPM), is presented in this work. According to the PPM, viscous and pressure forces acting on pseudo-particles are introduced. With this model, two numerical simulations of gas flowing around a circular cylinder are conducted at Re = 1.58 and Re = 30.92. Twin eddies in the downstream flow were observed at Re = 30.92. Simulation of gas flowing around a particle assembly is also performed, and the effect of structure heterogeneity on gas flow field is observed. As applications of the PPM to dynamic behavior simulation, bubbling phenomena with single and double orifices are computed, which shows the development process of bubbles formation near the orifice to the break-up at the bed top. Fluidization of multi-sized particles with the same density is also simulated, showing good agreement with experimental results.