Compared with the widely used emission wavelength of 532 nm, the atmospheric temperature observation using the emission wavelength of 355 nm requires higher precision of the spectroscopic spectrometer, and the line dispersion rate of the spectroscopic spectrometer should reach 0.1 nm/mm. A new high linear dispersion pure rotational Raman laser lidar spectrophotometer is proposed, which uses the double grating structure to achieve the purpose of laser lidar pure rotational Raman echo signal separation. Zemax software is used to design, simulation results show that the interval of 0.1 nm in two adjacent spectrum spectral optical system focus lens focal plane in the center of two adjacent line can be separated from 1 mm, which satisfies the requirement of line dispersion rate of temperature measuring pure rotational Raman spectroscopic spectrometer to reach 0.1 nm/mm. Comparing the experimental Stokes echo signal strength with theoretical calculation, the feasibility of the double grating spectrometer in the pure rotational Raman lidar is verified.