Through the analysis of Mapping Satellite-1′s photographic principle, geometric model was established to calibrate the intersection angle of the high-resolution, multispectral camera and three-line-array nadir camera in flight. And the correlative experiments using the image data of Mapping Satellite-1 were carried out. Result proves the method′s feasibility and high precision, and is close to the referenced result calibrated in laboratory on ground. Results′ difference of the intersection angle of high-resolution and three-line-array nadir camera is about 1′, multispectral and three-line-array nadir camera is about 5′. Meanwhile, the effect of the orbit determination error and the ground control points′ precision on the camera′s intersection angle is calculated and analyzed. The method is easily understood, and solves the problem that at present the intersection angle of Mapping Satellite-1′s high-resolution, multispectral camera and three-line-array nadir camera is only calibrated in laboratory on ground, cannot be accurately calibrated in-flight. It plays an important role in image fusion, rectification and advanced products′producing.