This paper counts and analyzes the effect of atmospheric dispersion on image resolution of 4 m optical telescope system. It is introduced that atmospheric dispersion will influence image resolution when the zenith angle is larger than 15°. With the zenith angle increasing, especially up to 45°, the image quality would be degraded greatly, so it is quite necessary that the atmospheric dispersion corrector(ADC) is applied to compensate atmospheric dispersion. By comparing the advantages and drawbacks of three modes for ADC:tilt mode, move mode and rotate mode, the glue prism pairs is used to eliminate the influence of atmospheric dispersion for 4 m telescope system, which would rotate with each other when the zenith angle changes. In 4 m telescope optical system, the ADC is positioned in front of imaging elements of collimated optical layout. Then we analyze the relation between zenith angle and rotating angle of ADC. The largest wedge angle of the ADC is 9.65°, and the rotating accuracy is ±0.1°, having an effect of 1/1 000 on resolution. So it is obviously concluded that the results satisfied the request of image resolution, and it is an effective way for the analysis of atmospheric dispersion and the application of ADC.