In view of intersection measurement, direction cosine algorithm is often adopted to calculate coordinates. In fact, because of error of optical equipment, two light rays from them don't intersect at one point; the direction cosine method is inaccurate in principle. In this paper, through analysis of spatial relationship among rays, target, and measuring accuracy of optical measurement equipment, etc., the weighted value of the shortest distance was taken as the target coordinate. Tests show that the improved direction cosine method is effective, resulting in higher accuracy.