The principle of measuring nighttime total atmospheric transmittance was analyzed and the equipment was developed to measure weak radiation atmospheric transmittance within any sky zone of elevation angle greater than 15° from level 0 to level 5 magnitude stars during the spectral band of 400 -750 nm, and the bandwidth of measurement was 30 nm. The method of automatically controlling CCD exposure time was used to obtain a sub-band weak radiation signal of stars, using image feedback mode to correct errors in the telescope searching-stars, which realized automatic unattended continuous observation all night. The equipment calibration adopted the combination of Langley - plot calibration method and multi-objective star calibration method. The measurement results were compared with the simulated values of CART and Modtran, which verified the feasibility of the measurement method and the reliability of the equipment.