To get rid of the burden of symmetrical installation of laser camera sensors in rail detection with laser non-contact test technology,a calibration method of visual system structure parameters based on coplanar method is proposed,which is called contour line calibration method. Firstly,the data of 140 points are extracted on the surface of standard block. Secondly,the data are processed through coordinate transformation,and Levenberg-Marquardt optimization algorithm is used to nonlinear iteration,which makes all points be on the same contour line. The calibration experimental results show that the repeat-ability accuracy of this method can reach 0.00133°,and detection precision can reach 7.7 μm. The method has advantages of simple operation and low requirements for equipment,and its high accuracy and convenience can meet the requirements of railway detection.