Roller plays an important role in rolling mill. However, the effective surface of roller is limited. After long time working, the surface of roller will wear. The roller wear will result in difficult controlling of shape and thickness of steel board. Further more, it can lead to the decline of product quality. So the measurement of roller wear is very urgent for rolling mill to ensure their product quality. In this paper, a measurement method for roller wear is introduced in detail. This method offers advantages of sensitivity, immediate response, electromagnetic interference, simplicity and non-contact. It can detect in the atrocious condition on-line and examine roller wear precisely and real time. It is an effective method at low cost instance. The basic principle of this system is optical reflection principle. In the paper, after explaining the principle of this measurement system, an error compensation algorithm is exactly calculated to improve accuracy of this measurement system. This algorithm is brought out to offset the shift of measurement track. And a simulation-software program is compiled with Microsoft Visual Basic 6.0 based on this principle. By using this simulation-software, the date of I/O signal for this system is gained. And the signal verse is automatically drawn in this software.