A miniature superradiant NH 3 optically pumped far infrared laser (OPFIRL) with or without buffer gas N 2 was theoretically studied. Base on the mechanism model of buffer gas, synthetical relaxation time was calculated. By solving the semi classic density matrix equations, spectra and the operating gas pressure of NH 3 superradiant OPFIRL with or without buffer gas N 2 were calculated. It was found that by adding buffer gas, FIR power could be raised, and there existed an optimum ratio of gases mixture and an optimum operating gas pressure which was higher than that of pure NH 3 operating.