This paper takes a long range oblique photography(LOROP) frame camera for an example.It deduces the whole course how to set up image motion mathematical model.Frame camera is a mode of operation for a tremendous increase in the across line of flight field of view.This causes that different field of view has different object distant,which results in heterogenic image motion vector on the film.It introduces mathematic demonstration about the reason of heterogenic image motion vector,analyzes the necessity of drift mechanism and puts forward a compensation method by using scan mirror,drift mechanism and exposure slit.At last,derives specific image motion compensation formula about depression and field of view.