A model of image motion velocity vector was deduced based on vector calculation and coordinate transformation. This model is suitable for both airborne and spaceborne camera. The influence of attitude angle attitude angular velocity and ellipticity of the earth on the image motion was taken into account in the model and a digital simulation was completed. The results indicate that: 1) The image motion velocity increases with the velocity of aircraft and decreases with the height of aircraft for the airborne camera; 2) The ellipticity of the earth plays an important part for image motion of the spaceborne camera and the error caused in near-polar is up to 4.60%; and 3) The attitude parameters have greater influence on the spaceborne camera than on the airborne camera.