The invention provides a positioning method and device based on the satellite-based augmentation of a Beidou No.3 satellite and a terminal. Current star clock correction parameters are estimated through star clock correction parameters historically released by the Beidou No.3 satellite, and current ephemeris correction parameters are estimated by historically released ephemeris correction parameters. The star clock and ephemeris of the Beidou No.3 satellite are corrected by the estimated star clock correction parameters and the estimated ephemeris correction parameters, the corrected star clock and ephemeris can be more close to actual star clock and ephemeris when the positioning is initiated, the errors of the corrected star clock and ephemeris relative to the actual star clock and ephemeris are reduced, and therefore, the positioning accuracy for the terminal is improved.