In response to the problems of poor adaptability of tree digging machines and low energy efficiency of hydraulic systems caused by dense forest planting and complex terrain in hilly and mountainous areas of China，the structure of the tree digging machine arm was designed and hydraulic cylinders model was selected，a co-simulation model of tree digging machine was established to analyze the structure and hydraulic system performance of the machine. Dynamic simulations were conducted on the chassis walking and arm of the tree digging machine using Recurdyn software. It was determined that the maximum lifting load of the tree digging machine was 2t. The maximum stress on the lifting arm was concentrated in the front of the lifting cylinder hole，with a maximum stress of 72.5 MPa. A co-simulation model of the tree digging machine-liquiddiscrete element method was established by using Recurdyn, AMESim, and EDEM software. The lifting condition of the tree digging machine，the soil cutting condition of the shovel, and the soil swinging condition were simulated and calculated. The pressure change curves inside the oil cylinder of each actuator and the soil cutting resistance change curve of the shovel were analyzed. The simulation results showed that during the lifting process of the arm，the pressure of the lifting oil cylinder was stable，with a pressure of 5.2 MPa. During the process of cutting soil，the resistance of the shovel was gradually increased, with a maximum resistance of 28 900 N. Under the condition of soil swing, the pressure inside the flap oil cylinder was increased with the increase of tilt angle, and the maximum pressure was 8 MPa. Testing on the hydraulic system of the tree digging machine in woodland was conducted, and the test results showed that the pressure of the lifting cylinder remained stable at 5.5 MPa during the lifting process of the arm. Under the condition of cutting soil，the pressure difference of the shovel cylinder was 10 MPa, and the indirectly calculated cutting resistance was 28 260 N. Under the swing condition of the soil, the pressure of the flap oil cylinder was increased with the increase of the tilt angle, and the maximum pressure was 7.7 MPa. Through comparative analysis of tree digging machine simulation experiments and hydraulic testing, the relative errors between simulation values and measured values under lifting, cutting soil, and soil swing conditions were found to be 5.5%，2.3%, and 3.9%, respectively. The accuracy of the cosimulation model of the tree digging machine and the stability of the tree digging machine arm structure and the hydraulic system was verified.