The invention provides a GPS (Global Positioning System)-aided mobile-terminal switching method for a time-division synchronous system. The method comprises the following steps of a, transmitting an observation sequence which is formed by connecting N identical sequence units with the time length of T in series by a base station, wherein the N is greater than or equal to 3; b, observing the observation sequence of an adjacent base station by a terminal at an observation window which is positioned in the middle of a local observation sequence and has the time length of T to obtain a measuring-time offset D1; c, acquiring own position coordinates by the terminal through a GPS, calculating the distance differences of the terminal and a local base station as well as the adjacent base station, and calculating a reference-time offset D2; d, forming a time-offset set by integral multiples of time values which differ from D1 by T within the range of +/-(N-1)*T/2, and selecting a time value of which the offset difference value from D2 does not exceed a preset threshold value as an actual time offset D3; initiating switching to a target base station according to D3 by the terminal.