To the breakage warning problem of grid fence, a grid breakage detection algorithm based on improved Harris corner is proposed. As traditional Harris corner extraction algorithm is very time-consuming, the parameter of gray “similarity” is introduced to demonstrate the gray similarity between pixel and its ambient pixels, through which to filter pseudo corners, reducing the Harris corner extraction time. Then after analyzing the corners' distribution, the breakage areas can be locked. Breakage detection experiments are taken to various fence images taken by robot, and the results indicate that the proposed algorithm is effective, and can meet the real-time requirements of fence breakage detection.