Abstract: A unified second-order-moment two-phase turbulence model (USM) is established for simulation of sudden expansion gas-solid flows in cooling combustor of rocket engine, based on Euler-Euler two phase flow method. In the model, k-εtwo equations are applied for modeling gas turbulence, Reynolds stress kpg equation is used for describing large-scale turbulent movement and small scale anisotropic characters of particles and interactions between gas and particles phase. The distribution behavior of the axial and radial mean velocities, fluctuation velocities and two-phase fluctuation axial velocity correlations of particles are simulated numerically and the results are found to agree with experiments well. It is shown that the axial fluctuation velocity of particles is larger than radial one, the gradient of the axial mean velocity affects the occurring position and the peak value of the fluctuation velocity. The axial component of the two-phase fluctuation velocity correlation is twice as the radial one.