Abstract: To predict nozzle erosion rate and study the chemical erosion in solid rocket motor nozzle, a dynamic erosion model was established by the chemical reaction and dynamic mesh, combined with secondary development on Fluent platform by UDF, and the two-way coupling effect of wall retrogression and internal flow field change of nozzle was realized. Under different propellant aluminum mass fractions, the dynamic erosion model was used to simulate the two dimensional unsteady fluid-solid-thermal coupling process of 70-lb BATES motor nozzle. The results show that, the calculated erosion rates are consistent with experimental data. The erosion rate decreases with the increase of aluminum mass fraction. The dynamic erosion model can predict nozzle erosion rate more accurately. The wall retrogression of nozzle surface changes the flow field and produces higher pressure and temperature near the throat. The concentrations of H₂O and CO₂ near the throat calculated by the dynamic erosion model are higher.