The invention discloses a method and a system for improving detection precision of a geologic radar for tunnel advance prediction The system comprises three signal receivers and a signal transmitter. The three signal receivers are arranged in the tunnel, and the signal transmitter is fixed on a radar antenna. The signal transmitter transmits the signal every millisecond and the position of the three signal receivers is fixed. The signal from the transmitter is processed by the processor and stored in a data memory. The stored signal information is converted into distance information by a computer, and then the three spherical surfaces are drawn by taking each signal receiver as the center of a ball and taking the corresponding distance as the radius. A point of intersection of the three spherical surfaces is a location of the radar antenna. The position point of the radar antenna is achieved per millisecond successively by means of a way of points into lines, and then a trajectory of the geological radar is confirmed and a precise prediction of unfavorable geologic bodies is realized.