In the imaging system, the calibration of nonlinear geometric distortion is still a problem. Based on the distortion model in which the radial geometric distortion is considered as the chief factor,a general correcting method that is independent of interior parameters of the imaging system,is given and discussed in this paper via a detailed analysis of the factors which largely influence the accurate measurement of distortion parameters. The experimental results indicate that the needed parameters to implement the calibration can be accurately determined by this method, and the calibration error is equivalent to the sample quantization error of CCD sensor.