The invention discloses a gravitation-assist simulation method considering an influence sphere of a target celestial body. Aiming at the disadvantages that when the ratio of the size of the influence sphere of a gravitation-assist target celestial body to the flying distance of a prober is relatively larger, larger analysis error can be brought if the motion of the prober in the influence sphere of the gravitation-assist target celestial body is ignored, the method simplifies the influence sphere of the gravitation-assist target celestial body into a sphere, and simplifies the motion of the prober in the influence sphere to two body motion along a hyperbolic orbit to analyze. The hyperbolic orbit and the prober orbit after the flight of the influence sphere flies are treated by adopting a conic curve splicing method to complete the stimulation analysis work before and after gravitation-assist flight, thus ensuring the stimulation analysis to be closer to the real motion situation of the prober in space.