Based on the optical rotatory dispersion and the isotropy of the sodium chlorate crystal, a new type of optical filter by internal reflection and optical rotation is firstly developed. Due to the speciality of the zero reflectivity when the linearly polarized light is reflected at Brewster angle, the optical filter can give a good filtering effect by using only a single polarizer. The filtering characteristics were analyzed by Mueller matrix and tested by experiment. The results show that the intensity of emitted red or green light can be continuously modulated by changing the angle of the polarizer. The extinction of green or red light appears when the rotation angle of the polarizer is respectively 133.36° or 173.06° relative to the initial position. The isolation of green and red can be about 10 dB.