The mathematical model of Forestry Felling & Cultivation Machine Transmission System describes the relationship between chassis transmission system and dynamic property by mathematical expression. Models reflect the relationships among the composing units of chassis transmission system, each units variable quantities and external environment elements. The mathematical model of Forestry Felling & Cultivation Machine Transmission System must be built before testing the performance of machine chassis through computer simulation. This paper mainly elaborates each composing unit of chassis dynamic transmission system and its mathematical models. Then, utilize MATLAB/ Simulink software to calculate and simulate its usability.