The use of a suitable gas distributor is essential for satisfactory performance of gas-solid fluidized-bed incinerators that are burning solid wastes. In the present study, the flow behavior of bubble and particles in bubbling fluidized beds with tubular distributor are performed using a two-fluid model. The computed instantaneous and time-averaged particle distributions, and the velocities of gas and particles, were analyzed. The effects of the jetting gas velocity and pipe spacing of tubular distributor on the quality of fluidization were investigated. The optimum pipe spacing is proposed to be in the range of 1.5-1.75, based on numerical results.