Abstract: Basic structure and working principle of round baler were expounded.Gear box was a key component of round baler，its mechanical characteristics was analyzed，stress and safety coefficient of gear case were obtained by finite element analysis based on SolidWorks Simulation. Analysis results showed that maximum stress point was 2.54×108 N，at reinforcing rib root of upper mounting surface，safety coefficient of maximum stress point was 1.22.Gear box shell safety coefficient should not be too small，it should be selected in range of 3~5，so reinforcing rib or material strength should be strengthened.A shell part that allows for light simplified design was determined，structure of gear box was optimized，and it could satisfy transmission power requirement.