Abstract. The NOAA-20 satellite was successfully launched on 18 November 2017. It carries five key instruments including Advanced Technology Microwave Sounder (ATMS). On January 31, 2018, the spacecraft performed a pitch-over maneuver operation, during which the two-dimensional lunar scan observations were collected. In this study, a technique has been developed by which the ATMS on-orbit geometric calibration accuracy can be validated based on this lunar scan dataset. The fully calibrated data are fitted in the antenna pattern coordinate by Gaussian function. The deviation of the center of the fit function from the origin of the frame is taken to be the boresight pointing error of the instrument. This deviation is further transformed to the Euler angle roll and pitch defined in spacecraft coordinate system. The estimated ATMS boresight pointing Euler angle roll (pitch) is 0.05°, (0.22°) at K-band, −0.07°, (0.25°) at Ka-band, 0.02°, (0.24°) at V-band, −0.07°, (−0.08°) at W-band, and −0.04°, (0.02°) at G-band. The results are validated by comparing with those derived from the coastline inflection point method. It shows that the Euler angles derived from these two independent methods are consistent very well. For the sounding channels where the coastline method is inapplicable, the lunar scan method is still capable of delivering reasonable estimations of their geometric calibration errors.