In order to resist the load at full load, the car body base will retain a certain upward flexural deformation when the rail vehicle is manufactured. It requires the surface profile of the base to be measured before laying aluminum honeycomb panels and floor glue. A method for measuring the surface shape of the car body base based on the principle of point target image measurement is proposed. This method uses a CMOS camera to measure the 4 LED on the car body base, in which 4 LED form a correlation Multi-target points. the LED target image gathered by CMOS camera is preprocessed by means of mean filtering, dynamic threshold binarization and contour extraction, and then the gray-centroid method is used to extract the positions of multiple light spots. By judging the position and size of each light spot, possible false target points or obstructions are eliminated, and different reference points are used for comparison according to the number of extracted light spots. When any LED target is obstructed, the center position of the LED target can still be solved effectively.It is shown by the experimental results that the maximum deviation of the center extraction of the LED target is less than 0.06 mm, which can fully meet the needs of vehicle body base surface measurement.