The invention provides a PPP-RTK positioning method based on a low-orbit constellation navigation augmentation system. The method includes the steps that direct transmission signals broadcasted by multi-system navigation satellites and low-orbit constellations are received to generate original observation data; navigation satellite augmentation information broadcasted by the low-orbit constellations and low-orbit satellite precise orbits and precise clock difference are received; precise point positioning is conducted by utilizing the navigation satellite augmentation information, the low-orbit satellite precise orbits and precise clock differences and the original observation data; or, when ground-based augmentation comprehensive error correction information is received, ground-based augmentation precise point positioning is conducted by comprehensively utilizing the navigation satellite augmentation information, the low-orbit satellite precise orbits and precise clock difference, theoriginal observation data and the ground-based augmentation comprehensive error correction information. By means of the method, near-real-time precise positioning, velocity measuring and timing results can be obtained in the globe, real-time centimeter-level positioning, velocity measuring and timing results can be obtained in ground-based augmentation regions, and seamless switching between ground-based augmentation regions and non-ground-based augmentation regions of the global region can be achieved.