An efficient approach for discrete particles coupled with the continuous fluid based on unstructured meshes is developed by reorganizing gas phase governing equations. The bubble formation caused by a single central jet pulse in a two-dimensional Pulsed Fluidized Bed (PFB) is simulated. The calculation results show good agreement with the experimental observations. Then our work concentrates on the study of the microscopic structures of two PFBs with different width. Pressure drop pulse and force chain breaks to overcome the inter-particle locking are found just as the jet starts. The simulations show that the gas flows in the bed experience from two-main-vortices to multi-vortices then to two-secondary-vortices. Particles in the bed demonstrate three types of characterized behaviors, i.e., raising, downslide along the bubble's boundary, and creeping motion in the corner.