A pure rotational Raman lidar for measuring atmospheric temperature on daytime is proposed. The quadruple frequency of 266.0 nm of Nd…YAG pulsed laser is selected as the transmitter wavelength, which avoids the effect of solar background light on the detection of atmospheric temperature. A new type of triple-diffraction double grating polychromator is designed as the spectroscopic system of lidar. Simulation results show that the designed double grating polychromator can achieve the extraction of Stokes and Anti-Stokes pure rotational Raman signals from high and low quantum number channels. The suppression rate of the Mie-Rayleigh scattering signals is up to 60-70 dB. Meanwhile, considering the effects of the ozone absorption and fluorescence on the detection performance of the system, the designed solar-blind ultraviolet pure rotational Raman lidar system with the analog detection mode can detect atmospheric temperature in the range of 2.2 km in 12 minutes' integration time.