Dispersion controllment is an important step in ultrafast optics. A reflection grism is introduced, which is composed of the prism and grating. The dispersion of the grism is analyzed with ray-tracing method, and the impact of grism structural parameters on the dispersion is discussed. As seen from the results, the second-order dispersion increases with the separation of the prism and grating, however, the third-order dispersion decreases. The separation of two grisms can be asymmetric in order to adjust the dispersion value of grism pair. The second-order dispersion of grism decreases with the incidence angle, and the third-order dispersion increases with the angle. When the grating constant is changed, grism dispersion corresponding changes. The separation of the grism-pair has little effect on the dispersion of grism. The results show that the dispersion of grism is heavily influenced by the separation of the prism and grating, incidence angle, and the grating constant. By adjusting the above parameters to change the dispersion of grism, it can meet the needs of ultrafast optics.