The invention relates to an existing railway measuring method based on LIDAR (Light Detection and Ranging) track point cloud data. The existing railway line measurement has the defects of poor flexibility and limited measuring length. The method comprises the following steps: recording continuous three-dimensional coordinate data in a track running process by using a vehicle-mounted LIDAR measurement instrument for serving as track point cloud data; extracting a center line between two tracks, translating o obtain a route center line, and calculating the fixed-length chord slope of the route center line: evaluating the slope by taking new data serving as a point set as a difference, generating a fixed-length chord slope sequence, and filtering; picking segmentation points on the basis of the smooth fixed-length chord slope, and decomposing a continuous route into curve units; evaluating the intersection points among the curves according to front and back intermediate straight lines of each unit, fitting the radius and circle center of a circular curve part of the route, and resolving a corresponding route parameter and mileage. A basic unit set of route curve elements is constructed according to the LIDAR track point cloud data, so that the aims of route reconstruction and retesting are fulfilled, high flexibility, high measuring efficiency and a simple process are realized, and measured data is accurate and reliable.