In order to accurately predict the influence of the multi-physical field coupling in the plunger chamber on the fuel supply process of the fuel injection system under high pressure environment,the thermal-fluid-solid multi physical field coupling model was established based on the models of the plunger chamber,the plunger pair leakage and the fuel physical characteristics.Its high accuracy was verified through the decoupling calculation and test analysis.The results of the numerical analysis show that the larger the plunger diameter is,the smaller the residual volume is,the greater the increase rate of the fuel pressure in the plunger chamber is; when increasing the initial sealing length of the plunger pair,reducing the initial clearance of the plunger pair or increasing the cam speed, the impact on the oil supply process is little due to the less leakage of the plunger pair; the lower the initial temperature of the fuel is,the greater the bulk elasticity modulus and density of the fuel are,resulting in the faster increase rate of fuel pressure in the plunger chamber.