SiC crystals are used for a high refractive index material, as the frequency-selected device of Brewster plate. A stable single- longitudinal- mode green laser with an output power of 120 mW is achieved. Both the theoretical analysis and experimental results show that, compared with the common frequency-selected device using K9 glass as Brewster plate, the new frequency-selected device using the high refractive crystal of SiC as Brewster plate makes it easier to adjust the entire optical system. Moreover, the device works more stably, be much easier to achieve commercialization.