The operating characteristics of optically pumped CH3OH FIR lasers have been studied with both open cavity and dielectric waveguide cavity. Lasing oscillations on 70.6, 118.8, 392, 418 and 570.5±m were obtained and output power at 118.8?m and 570.5±m were 12.6 and 3.5mW respectively. The wavelength of the far infrared laser were measured by means of scanning cavity length and scanning Fabry-Perofc interferometer, the precision was up to ±0.5μm.