This paper presents a new calibration method of line scan camera model based on cross-ratio invariance using a calibration pattern on the top of the gauge block. Instead of using the 3D pattern, planner pattern with precise motion platform, or pre-calibrated matrix camera, only a planner pattern with gauge blocks is used in this new method. A group of data on the line scan camera projection plane is obtained by placing the planner pattern at a different height. Line scan camera parameters were calibrated through a derived mathematical model. This method is simple, inexpensive and easy to use. The experimental results demonstrated that the average reprojection error of this method is 0.0431, which is 62.2% lower than the traditional method, which proves the feasibility and effectiveness of this method.