Abstract: A fast precision measurement method for the existing railway based on the GNSS／INS integrated technique is presented in this paper. The system consists of the IMU, GNSS module, odometer and track gage sensors carried on the railway track trolley. In the surveying process, GNSS／INS system calculates the precise coordinates of track midline by using the carrier coordinates, attitude and gauge information. This method uses the rapid mobile surveying model and does not depend on the high precision track control network. The results of field tests on the XUZheng highspeed railway nonballastedtrack show that the measuring errors are less than 6 mm (RMS) and 15 mm (RMS) in the horizontal and vertical directions. And this method can be used for the recovery of existing railway.