The binocular stereovision is a primary approach to realize optical passive 3-D measurement. To search corresponding points fast and accurately, the stereo pairs must be rectified. A method is presented to rectify stereo pairs without calibration for cameras. In this method the initial values of perspective projective matrix; rotative matrix and translative matrix are calculated from the fundamental matrix, than these matrices are optimized based on the coordinate value of corresponding points. This method can avoid the local least value in the optimal calculation effectively, and the dependence on the calculation precision of the fundamental matrix excessively. By the experiment of image rectification to compare this method put forward this here with two typical methods that one depend on fundamental matrix calculation and the other dispenses with fundamental matrix calculation, it is shown that this method can rectify stereo pairs fast and accurately, but bring little image distortion.