Abstract: In order to measure the rail linearity accurately,an embedded laser detection system,composed of image acquisition and transmission module,image processing and data-processing module,laser range module,was designed based on autocollimation theory.After a series of image processing,the images and distance parameters were sent to the autocollimation algorithm,and the rail linearity offset can be obtained with a measuring accuracy of 0.3 mm.The system can replace the traditional manner of rail detection,also make the detection process more simple and accurate.