Presently inspecting method of crane rail had a poor measuring accuracy and lower operation efficiency. An auto-inspection system for the rail of cranes was presented in this paper, which could be helpful to improve measuring accuracy and operation efficiency. A laser scanner was used in the system to trace the position of the robot in time. And the central line of railway could be rebuilt by using the data collected by the laser scanner, which could evaluate the shape of the rail automatically based on the mathematic model of the system. The measurement accuracy of the inspection system could meet the requirement of relevant standards, and the operation efficiency was improved in a high degree. (4 pages)