Abstract: The environment issue has been more and more serious than ever before along with the increasing numbers of tractors. Different from pure electric tractors, medium-sized tractor more widely adopt hybrid power driver according to the machine structure and operation characteristics. The Hybrid Electric Tractor (HET) is capable of enabling the diesel works in an optimal area by controlling the output torque of engine and electronic motor to achieve fuel economy and emission reduction. Designing the parallel hybrid tractor transmission system and control method are put forward in a 66kW off-road tractor based on the plowing operation cycle condition. The overall power should meet the maximum power of the plowing operation with the power balance equation. The control strategies are established by road transport modes and field operating modes, respectively. A logic fuzzy control system to Degree of Hybridization (DOH) on account of the output torque and State of Charge (SOC) is introduced. Aiming at the fuel economy parameter, the optimization design shows that the hybrid tractor can improve 19.2% of fuel economy between SOC 0.4~0.7 compared with the traditional tractor.