The influence of the sealing performance of needle couples on the operating reliability of fuel injector was analyzed with the PressureTime injector as the study object.Aimed at the leakage of fuel between needle valve and valve body of PressureTime injector,based on the theory of fluid dynamics and tribology,the oil film thickness of the needle valve,the valve body of PressureTime injector and between of them was calculated by bidirectional fluidsolid coupling method,the oil film thickness and the leakage of fuel under different fuel temperature and initial load were compared.The results indicate that the leakage rate is increased with the increasing of differential pressure on both sides of the oil film,the fuel temperature and the eccentricity of the needle valve.With the increasing of fuel temperature and deflection moment,the film thickness ratio is decreased,and the lubrication condition of the needle couplings becomes worse.The end face of the needle valve is prone to wear due to the lower film thickness ratio.