Aiming at the designed spinning prism Q-switch, the refractive index of the prism was considered for the first time in the optical acceleration, and the influence of the index of the prism was calculated in detail based on the theory of fourfold optical acceleration. The calculated results show that compared with the flat mirror, the rotating speed of the prism will “diminish” when the refractive index is considered, which means that the smaller refractive index of the prism have better optical acceleration. In one word, the refractive index of the prism has negative influence on the optical acceleration. Therefore, in the design of the optical acceleration device, the refractive index of the prism should be considered carefully in order to obtain the best optical acceleration.