A safety zone expansion guidance method for avoiding obstacles in planet landing disclosed by the invention belongs to the field of deep space exploration. The method includes the following steps: defining a landing point fixed connection coordinate system and an error ellipsoid spindle coordinate system; building a landing dynamics equation under the landing point fixed connection coordinate system; determining an ellipsoid expansion safety zone according to the position error n(sigma) ellipsoid of a detector, and calculating the safety distance index value of the detector relative to an obstacle; and constructing a Lyapunov function based on the state of the detector and the safety distance index value of the detector relative to the obstacle, designing an obstacle avoiding guidance lawbased on the Lyapunov stability principle, and using an acceleration command a to control the landing track of the detector in order to reduce the influence of the multi-disturbance and uncertain environment on the planet surface on the obstacle avoiding guidance of the detector, thus avoiding the obstacle on the planet surface and realizing autonomous safe precision landing. The control acceleration command is analytic. The method does not contain complex operations such as integration, meets the requirement for real-time online feedback control, and is conducive to engineering application.