In order to improve the centering precision of non-diffraction laser beam, a sub-pixel edge detection method of bright ring is proposed. The pixel roof edge points of a bright ring were detected based on maximum intensity in a local region firstly. These pixel edge points were then processed by linear interpolation to get sub-pixel edge points. Finally, the center of the laser image was calculated by using the least square method of all these sub-pixel edge points. For 50 samples captured (with a 640 pixels×480 pixels camera and 0.057 2 mm/pixel as resolution of the target) at each position at different distance of 40 m, 50 m and 60 m, the standard deviation for center fitting of the method with sub-pixel edge points was 0.021 4 mm, 0.037 2 mm and 0.042 3 mm for x, and 0.022 8 mm, 0.035 1 mm and 0.043 7 mm for y, respectively, much better than that with pixel edge points. Experiment results show that the method is feasible.