Abstract: A practical linear approach for camera calibration was proposed on the camera model with radial lens distortion to solve the problem of instability in the nonlinear calibration. Firstly, order radial lens distortion parameters are computed by using cross ratio invariability. Then other parameters are calibrated linearly based on a homographic metric and two basic constraints of intrinsic parameters. Experiments show that the new approach is efficient, accurate and robust, which can satisfy accuracy requirements of industrial machine vision.