Abstract: The all-sky imager is an important ground-based auroral observation equipment. Accurate optical geometric correspondence between "object-image" is the foundation for obtaining the structural scale of auroras and achieving joint observations between the all-sky imager and satellites. This paper proposes a geometric calibration method for all-sky imagers based on gradient descent and star maps. This method determines the coordinates of each star point in the star map within the all-sky image, and uses gradient descent to determine the pixel position of the zenith in the all-sky image, as well as the relationship between the imaging radius and zenith angle within the field of view. 26 and 22 star points were marked in all-sky images taken at two different times, respectively, and the calibration results were verified by comparing them with the corresponding star maps. The verification results showed that the absolute values of the stellar azimuth angle errors were 0.1547° and 0.2062° on average, and the absolute values of the zenith angle errors were 0.1076° and 0.1133° on average, respectively. This indicates that the calibration method proposed in this paper is accurate and effective.