To precisely calculate geometric parameters of large field view space camera, such as object distance, projection angle, ground sampling distance, swath width, the precise calculation method of above-mentioned geometric parameters was studied，including nadir imaging and rolling imaging. Considering earth curvature and projection angle, geometric model was constructed, the calculation method was improved to heighten precision. The analysis shows that, for a large field of view space camera on 650 km orbit altitude, with 20° half field of view and 20° roll, the maximum GSDx is 2.31 times of the minimum GSDx, is 1.78 times of the approximate GSDx. The maximum GSDy will become 7.16 times the minimum GSDx, is 4.29 times of the approximate GSDy. The swath width is 1.33 times of the approximate swath width. Therefore, the traditional calculation method is inaccurate, the precise calculation method of geometric parameters in this paper is useful for the imaging quality.