A fast ellipse center computation algorithm is proposed for optical power-meter to make it highly-accurate and fast, considering that the spots of optical power-meter may be deformed, partial absent or double reflected and the goal of the spot calculation is just to obtain the centroid. The edge of the measured spot is obtained by bi-value morphology. With improved RANSAC method, the false edge points are eliminated for ellipse fitting. And the center of the ellipse, which is also the center of the measured spot, is directly calculated from the fitted coefficient of the ellipse. Experimental result shows that, when applied to optical power-meter, the proposed algorithm is fast and as accurate as the traditional Hough Transform – 0.01D and it is suitable for practical application.