Abstract A highly optimized dynamic Monte Carlo program TAMIX has been developed to simulate the ion beam mixing process. In addition to the collisional features, some of the diffusional processes are taken into account in TAMIX for elevated temperature irradiation applications. TAMIX can be run in three modes, i.e. Static mode, collisional dynamic mode, and collisional-diffusional dynamic mode. TAMIX is a non-analog vectorized Monte Carlo program for the full use of the capability of vector computers such as the Cray. In TAMIX, sophisticated models have been adopted to obtain both speed and accuracy, including tabulation of the scattering angles, energy-dependent mean free path for nuclear collisions, “random surface model” for sputtering, and concentration-dependent surface binding energies. The simulation results applied to a wide range of situations show good agreement with experimental data.