A new sub-pixel algorithm based on the principle of the parabola fitting is proposed. According to the condition of the correlation peak,the outline of the longitudinal section along the climax of the correlation peak is fitted by parabola. The longitudinal section is executed along different direction to acquire different parabola,and then the climax of parabola can be gained from every parabola. The optimum position is the point,where the sum of distance is the least from it to all other points. Thus,it is realized that the line of parabola is described by point and the surface of correlation peak is described by line,which can show more truly the condition of the correlation peak. The experimental results show that the algorithm maintains a high precision of the subpixel extraction.