Abstract: In this paper, aa approach is proposed for estimating jacket launching angle．The launching angle is the included angle between the jacket's bottom line and sea, aa very important parameter for the launching．First, athe approach computes the homography and the vanishing line of the up-surface on the jacket via the feature points in the up-surface．Then, athe image of the absolute conic is computed by those homographies computed at different launching instants．At last, athe launching angle is derived from the vanishing line, athe image of the absolute conic and the horizon in the image．The major measurement errors are also analyzed by simulated experiments．The experimental results demonstrate the feasibility of our proposed approach．