As the important resource of biomas energy convension and feed utilization, corn stalk needs to be smashed to improve the effective utilization rate. In order to study the performance of hammer mill for corn stalk, the process and performance of smashing corn stalk was studied by hammer mill. Based on the analysis of smashing process by high-speed photography, main smashing types of corn stalk were decided as following: impact smashing, hit smashing and rub smashing, and the impact smashing and rub smashing had greater influences, it could be obtained that the linear velocity of the hammer (the rotation speed) and moisture content of corn stalk had greater influences on the smashing performance of the hammer mill. Then, the main factors that affected the smashing performance of hammer mill (the rotation speed, moisture content of corn stalk and screen size) were chosen as the experimental factors, the output per kW·h was decided as the evaluation index, and experiments were conducted. The experimental results showed that the sequence of various factors’ influence on the output per kW·h was screen size, moisture content of corn stalk and the rotation speed. Parameters were optimized based on regression models. With the maximum output per kW·h as the optimization object, the ranges of the factors were chosen as follows: the moisture content of 10%~50%, the rotation speed of 2000~3500r/min and the screen size was 6mm. Parameter optimization results showed that when the moisture content of corn stalk was 10%~32%, the rotation speed was 2000r/min, when the moisture content of corn stalk was 33%~50%, the rotation speed was 2020~2452r/min, and the rotation speed was increased with the increase of moisture content of corn stalk. The research can provide theoretical and technical basis for design of hammer mill for corn stalk.