The invention discloses a landing dynamic simulation system of a small celestial body probe. The system comprises a probe parameter editor, a small celestial body gravity computing engine, a dynamic computing engine and an API binding layer; the small celestial body gravity computing engine completes the computation of current gravitational acceleration of the probe according to a three-position polyhedron model or spherical harmonic coefficient parameters of the target celestial body; the dynamic computing engine generates a 3-freedom-degree/6-freedom-degree dynamic model of the probe according to the current parameter configuration, completes the motion and posture computation of the probe together with the small celestial body gravity computing engine according to the related data of an engine controlling quantity, an ephemeris database and a celestial body parameter database input via the API interface binding layer, and returns to a client program via the API interface binding layer, and at last the landing dynamic simulation of the small celestial body probe is completed, thus the client can call the simulation system via different language interfaces to transmit the related data.