Abstract: Abstract: In recent years, corn has become the first major crop in place of wheat and rice, which has an important influence on the national life with its production increasing. Corn snapping device is a main component of corn harvesting machine, and has an important effect on the quality of corn harvest. Currently, according to the way of working, there are 2 types of snapping devices: snapping rolls and plate type. The existing snapping device is easy to cause the corn ear nibbling and grain loss. In order to solve the above problems, the test device of corn ear picking by pulling stack upwards was studied, the principle of which was imitating artificial snapping action, and pulling stalk upwards to pick corn. It mainly included corn ear picking device, clamping feeding device, corn roots cutting device, high-speed photography and computer data acquisition system. When corn plant was fed to the ear picking device by the clamping feeding device, the corn stalks were cut off through the corn roots cutting device, then the snapping rollers pulled up the corn stalks and the corn ear encountered the snapping rollers, and finally the corn ear was bent and broken off. In the process of picking corn ears, the force of stalk was a resultant force of the force of pick ear buckle and the force along spiral line, which made stalk move backward and upward. This paper also analyzed the force relationship of corn ear. When the corn ear encountered the snapping rollers, the snapping rollers only overcame connection force and connection torque to bend and break off the corn ear. The test was done at the laboratory of agricultural machinery. The grain moisture content was 21%, and the grain loss rate was taken as the index to estimate the performance of the harvesting device. Through the single factor experiment, the impacts of the roll's rotational speed, the roll's interval and the angle between roll and horizontal surface on the rate of grain loss were analyzed. The process of harvesting was captured through the high-speed photography, which was helpful to the comprehensive analysis in the late period. Through the single factor experiment and the analysis of variance, it was found that the grain loss rate reduced at first and then increased gradually, when the rotational speed was changed in 6 levels of 500, 600, 700, 800, 900 and 1000 r/min in turn and other factors were changeless. The rotational speed had significant effect on the grain loss by the analysis of variance. The average grain loss rate was the least (0.293%) when the rotational speed was 700 r/min. When the roll's interval was selected to 5 levels including 4, 6, 8, 10 and 12 mm in turn, the grain loss rate was decreasing gradually in general. The grain loss rate was the least when the roll's interval was 10 mm, which was 0.33%. But, if the interval was too large, it had some problems such as the grasping ability was weakened and the corn head was gripped. The effect of the angle between roll and horizontal surface on the grain loss rate was not obvious, which was set at 5 levels of 0°, 10°, 20°, 30° and 40°, and the grain loss rate was 0.28%-0.31%. It was found that corn ear picking by pulling stalk upwards had good performance, and the corn grain loss rate was less than the national industry standard (2%) and also less than the traditional snapping roller. This way of picking corn can improve the corn grain quality and reduce the grain loss, and provide a thought for corn harvesting.