Abstract: This paper solved a Phobos gravity field model with degree of 80 by using shape forward modeling method. We introduced three methods that are edge, surface, polyhedron, to generate integral unit and obtain outside potential value from shape model. During computation we rotated the reference coordinate system of the polyhedron model into the principal axis frame. The potential varies from 45-56 m²/s², basically showing a stripped distribution and indicating a maximal value around the Stickney crater. Meantime, the moment of inertia in x, y, z axes, with values of 0.355 45, 0.418 10, 0.491 34 are obtained; the spherical coefficient C₂₀ value is -0.029 395 4, and C₂₂ value is 0.015 254. By comparing the acceleration of 20, 50 and 80 degrees gravitational potential fields, we can confirm that the benefits of higher degree of the gravity field can be seen on acceleration.