The hydraulic system principle of the twinwheel trench cutter milling device was introduced. The simulation model was built of an entire milling wheel device hydraulic system by using AMESim software. According to the design requirements of the relevant parameters, the eight different opening degrees of a main valve port were set. Under external input conditions of both high load and low load, the changes of motor flow and pump pressure were analyzed along with time. A reference and basis are provided for the design of twinwheel trench cutter hydraulic system.