The direct measurement of exterior orientations using the integrated IMU/DGPS system proves to be an effective means. Experiments show that the accurate performance of direct orientation measurement is sufficient for forming orthophotos and small or medium scale maps. Aimed at solving the problems existent in the IMU/DGPS orientation module, this paper deals with the integrated IMU/DGPS system and the elements of IMU/DGPS-based photogrammetry and, on such a basis, emphatically analyzes the overall system calibration.