A novel calibration method to determine all the primitive parameters of the stereo visual sensor with free-position planar pattern is proposed. In this method, without restriction to the moving of the planar reference object ,all the camera parameters can be readily calibrated with the mathematical model of lens distortion. And based on the 3-D measurement model of stereo-visual sensor, the parameters of sensor can be optimized with the feature points constraint simultaneously. The proposed approach greatly reduces the cost of the calibration equipment,and it is flexible and practical in the visual measurement. It is shown that this method has high precision by experiment,and the measured relative error of space length excels 0.3 %.