The current corn classification is mainly handicraft. This method is low efficiency, labor intensive, and has failed to meet the requirements of production. This system unifies PAC and machine vision, designed a corn grading system. The whole system has configuration monitored and controlled by using machine PAC visual technology and Device Net field bus technology, the system has a safe and reliable operation, classicists accurately and rapidly. This system can significantly improve the efficiency and frozen corn sorted product quality, sort and speed over40 per minute, sorting accuracy can reach more than 99 percents. Demonstrates PAC technology in sorting system unique flexibility and expansibility, better realize the controlled object of automation control, has wide application prospects.