The flow stress behavior of Ag/SnO2 composite under different deformation condition was investigated by isothermal constant speed compression test, and then the parameters of the kinetic equation of dynamic recrystallization and the equation of the recrystallized grain size were identified according to the experimental data. By finite element simulation of extrusion process, the grain-size evolution and final grain size of Ag/SnO2 composite by reactive synthesis were obtained. Compared with SEM images of extruded sample, it is found that the process simulation is well consistent with the experiment. Finally, the change mechanism and characteristic for the grain size in the extrusion process were revealed.