Replacement and extrapolation combined navigation method

The invention discloses a replacement and extrapolation combined landing navigation method which is suitable for height and speed navigation in the landing process of an extraterrestrial celestial body of a space detector. The method comprises the following steps of: determining the landing altitude and speed of the detector in a landing preliminary stage by adopting a method in which the inertial navigation and a measuring sensor are in a weighting eclectic manner; and directly determining the landing altitude and speed of the detector by adopting measuring information of the measuring sensor below the specific height of a landing terminal stage, and determining the height and speed in an updating interval of the measuring information by adopting the inertial navigation extrapolation. The method is used, the navigation accuracy of the landing altitude and speed is obviously improved, and the replacement rate and the data smoothing property of navigation data of the detector are guaranteed.