Aiming at the status that the mechanism study of the chopper device in sugarcane harvester is insufficient，chopping loss is high, and the requirements to the chopper device present the character of diversification, three different harvest processes varied in the mounting position of the chopper device were compared and analyzed, including frontmounted, centralmounted and rearmounted. Based on the analysis result of the merit and demerit between different harvest processes, the viewpoint that the harvest process which adopted frontmounted structure of chopper device was more suitable for the bending and lodging sugarcane in China was proposed. Further theoretical analysis of the frontmounted structure was conducted and empirical formula of billet length produced under this structure was deduced. Based on this, a chopper testing unit was designed, as well as a new type header of sugarcane harvester charactered by frontmounter chopper. A highspeed photography test was conducted on the testing unit and law of motion of billets and canestalk was observed, as well as the separation process between stalk and leaf, furthermore, sugar loss during chopping process was analyzed through the procedure of fracture formation. Taking the billet acceptability as index, and through orthogonal field test conducted on the header, the factors impacted on billet quality were optimized, and the billet acceptability reached up to 93% under the condition that intersect depth was 4mm, ground speed was 2km/h，and rotational speed of rollers was 300r/min. By means of billet length test and statistical analysis, a conclusion was drawn that billet length was approximately in normal distribution, and the length coefficient in aforesaid formula was deduced as 0.7.