Abstract: X-ray digital imaging system is applied to industrial Non Destructive Testing fields widely.Resolution is the most important technology index in the whole system,which directly determines detecting precision and application scope of the system.This paper introduced various components of the imaging system as a starting point,analyzed each component and the whole system's resolution,discussed relationship between resolution and magnification of the system and drew their function curves.Finally,it explains how to build high resolution X-ray digital imaging system illustrated by the case of BGA solder joints of X-ray automatic inspection in electronic industry.