The Loaders’ hydraulic transmission system trends towards medium and high-pressure. The research object of this paper is thermal equilibrium of new quantitative medium and high-pressure hydraulic system of type 50 of wheel loader, which is developed by Xiamen Xia Gong (XG) Machinery Co., Ltd. (abbreviated as XGMA). Aim is to research the thermal equilibrium of loader’s hydraulic system before increasing the pressure at 16MPa and prove the simulation results reliability through experiment (max error is 11.57%). The simulation results are thought to be reliable, after ignoring some disturbance factors existing in the practical work. Consequently, loader's thermal equilibrium have been done after increasing pressure to 20MPa, the results of research show that thermal equilibrium will be obviously optimized, it will drop power loss (drop 17%) and improve hydraulic system’s reliability and reduce the cost after pressure was raised.