A quick and high-precision image center locating algorithm based on the difference between the corresponding ellipse′s long and short axe method was proposed ,to meeting the requirements for high precision and time-saving in real time beam automatic alignment process of the high power laser device. The maximum value of the spot′s area is obtained by acting the Big Law Method, 3×3 Neighborhood Method and Eight-Neighborhood Method on the spot image in turn;Lengths of the long and the short axis are obtained by the analyzing the center distance of the maximum spot, and adjust the spot shape by the deviation of the ellipse′s long and short axe until to the deviation approach to zero;Through analysis the deviation between the actual spot center and the corresponding reference position, the adjusting steps of stepping motor controlled by the closed-loop control method is obtained, and the automatic alignment is realized. This algorithm is verified in the high-power laser device, the experiment results shows that the alignment time of the main amplification of the optical path is shortened to 15 min, the near-field alignment accuracy is better than 0.2%, and the far-field pointing accuracy is better than 1 μrad, all of them meet the alignment requirements of the high-power laser device.