The problem of inconsistent positive and negative output torque of hydraulic travel motor of an excavator was studied,the main reason for the inconsistency of the positive and negative output torque of the motor was the large differential pressure between inlet and outlet,and the main factor leading to large pressure difference deviation of the positive and negative of the motor was the dimensional tolerance of the valve port in balance valve was inconsistent.The dimension chain model of motor balance valve port was established,the influence factors about dimension tolerance of the balance valve port,such as valve core,spring seat,valve head and end cover groove,were analyzed.With CFD simulation and optimization design of the each valve port dimension chain,combined with the actual processing difficulty of parts,the tolerance distribution was carried out,so the valve port size of the motor oil return balance valve was kept at 0.5~0.7 mm,and then the variation range of motor back pressure was reduced.The test results show that the optimized dimension tolerance of motor balance valve keeps the consistency of the differential pressure between the inlet and outlet,thus the consistency of the positive and negative output torque of the motor is ensured.