Numerical simulations of gas-solid two-phase in tail-pipe nozzle were carried out using particle trajectory model. The simulation results were compared with that under the situation of pure gas. The particle trajectories and parameters in internal flow were studied when particles' diameter changed in the range of 1µm to 100μm. The result shows that the addition of particle phase influences the internal flow field. The trajectory of particle varies with the diameter of particle. The particle concentration and accretion are related to the trajectory of particles. These conclusions may be of certain importance to the thermal-protection of tail-pipe nozzle.