In order to realize the accurate superposition and seamless image assembly of interleaving assembly time delay integration (TDI) CCD imaging under the condition of large lateral swing space in spaceflight camera, it is mentioned in this paper that the number of the minimum overlap pixels can be calculated with the angle of image motion velocity vector among the dislocation lap joint pixels. First, velocity vector of ground object target in the coordinates of surface feature during satellite lateral swing imaging is analyzed. The velocity vector, latitude and longitude of harmony feature point are calculated using lateral swing angle. Then, the relationship of imaging and physical parameters have been projected to the image plane coordinates using the method of ray tracing and vector mapping. And then the angle between imaging velocity of overlap pixel has been calculated. Finally the least lap number pixel of two adjacent pieces TDI CCD is established by TDI CCD relationship. The algorithm is applied to the Fast Boat One satellite. By comparing the experimental and theoretical results, a deviation of pixels exists between actual and theoretical values in the image registration accuracy range. This method can effectively eliminate the large side swing imaging dislocation lap on pixel precision of stitching.