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.