The precision of CCD calibration depends on both distortion models in imagery process and signal-noise-ratio.The former is called intrinsic factor

and the latter is called extrinsic factor.The paper presents to select distortion model using statistic notable check and correlation coefficient check

and use signal-noise-ratio

which is a proportion of distortions in data noise

as criterion.A large number of simulative and realistic experiments show（1） Various distortion models exist in various imagery system;（2）There is high correlation among distortion parameters or between distortion parameters and camera parameters;In addition

（3） The larger the signal-tonoise ratio is

the larger the compensation capability to distortion is

on the contrary

the smaller the ratio of signal-to-noise is

the smaller the compensation capability is;（4）The relation of precision improving with signal-to-noise ratio is exponential function.