Optimal nonlinear weighting method for light-spot positioning is an improved barycenter algorithm.In view of its complexity and enormous calculation for calculating optimal weighting coefficient,an easy method is proposed.The optimal coefficient of different light-spot is studied with large numbers of data in this method.The result shows that the optimal coefficient is independent of the power of noise and could be applied to the positioning of ordinary light-spot.Moreover,the optimal coefficient is ascertained as 2.15.Compared with other sub-pixel algorithm,the weighting barycenter algorithm based on the optimal coefficient reduces the error by 1/3,and the result is satisfying.