A new method of non-metric camera distortion calibration is proposed, independent of the known imaging center, which is fit for the second order polynomial distortion calibration model. This method is made up of the following two steps. First, the curves distorted from straight lines are closed by adding straight-line segments, and areas of those curves are computed. Sencond, the relationship between these areas with ends and the distortion parameters with center are elicited, thus the approximate values of parameters are resolved. The above relationship is iteratively modified by the reference values according to the distortion model, based on the endpoints of these curves and the current calibration. Therefore, the distortion parameters and center are iteratively approaching the real values. Moreover, a target function of distortion calibration is designed, with local nonlinear optimization method, so as to reduce the image noise′s effect on calibration. Both simulations and real image tests show that this method can implement exact calibration with fast convergence.