A device for testing the performance of snapping rolls of corn harvester was researched and developed, and the influencing factors on picking maize-cob were discussed in this paper. In the designing of the tester, the regulating and controlling factors influencing the roller-type picking mechanism were considered. The working factors can be adjusted and controlled in monofactorial tests and multifactorial tests. The snapping rolls of main corn harvester made in China can be installed easily. The affecting factors of the snapping rolls on corn-grain gnawing damage were analyzed by tests. The results show that the rotate speed of the snapping rolls is the key factor on the condition of a certain roller type.