A new method of extracting the center of interference fringes is proposed based on polynomial fitting,which is named as the polynomial fitting method along the normal direction of fringe edges. According to fringe gray distribution,firstly the interferograms are compressed to 2 gray-level images,and the fringe edges are extracted. Secondly, by fitting the data of fringe edges with polynomials, the normal direction of the edges is defined. Then based on the characteristics of fringe gray cosine distribution, the extremum is obtained by using least square method to fit the gray data of fringes along the normal direction ,and the coordinate of the center is obtained. This method is good at measurement precision and has anti-jamming power. It has been proved that this method is fit for the parallel linable fringes and the interferograms with the arbitrary closed loop fringe pattern.