A new algorithm for automatic interpretation of interference fringes is proposed,which uses their own gray characters and designs an appropriate weight function,then solves a series of curves to which the integrals of the square of the distance from each point of the fringes is minimal,that is to say,resolves expectations of fringes under the weight function designed.Furthermore the new algorithm has the functions of extracting the multiplicity of fringes as well as image processing.And the algorithm is insensitive to the random noise when the weight function is an odd function of gray of an image.