By accurately measuring the displacement between the roller surface and the optical fiber probe relative to a null position, we can test the roller wear. The whole testing method and system were introduced. Each part of the testing system was illustrated. And also a novel fiber-optic sensor with three probes in equal transverse space is adopted. Using this sensor, the effects of fluctuations in the light source, reflectivity changing of target surface and the intensity losses in the fiber lines are automatically compensated. This method offers such advantages as non - contact, no electromagnetic interference, simplicity, low cost, high sensitivity, good accuracy and stability.