In order to meet the real-time demand in on-machine inspection of machining center and calibrate the parameters of line structured-light plane with high efficiency, low-cost and high precision, a calibration method of light plane was proposed based on the planar target with concentric circles. Through moving freely the planar target at several arbitrary positions in the field of the camera′s view, 3D coordinates of points on the line structured-light plane could be calculated by the calibration method integrated with the model of perspective-three-points (P3P) and the principle of cross-ratio invariance, then the equation of the line structured-light plane was fitted by least square method(LSM). Experiments showed the method′s validity and feasibility by the analysis of calibration and inspection accuracy. It concludes that the method is suitable for the machining and inspecting field calibration with advantages in its simple algorithm and the flexible calibration process.