The injector needle valve couples is one of the three big precision couplings of diesel fuel injection system,and its sealing cone surface is prone to become invalid because of wear and tear during the working process.Theoretic analysis of the wear performance of the seal cone surface was carried out.It is shown that the wear of sealing cone surface is mainly caused by comprehensive function of the impact of the needle valve seat and impurity in the diesel oil.The sealing cone surface is deformed after wear,which causes the increasing of surface roughness and the lowering of sealing effects.The experimental study of the injector was carried out in the test bench of engine,and the scanning electron microscopy (SEM) was used to analyze the worn morphology of sealing cone surface and its wear mechanism.The experimental result shows that along with the increasing of time usage,there is obvious wear on the surface of needle valve,then clear scratches and a large area of spalling appear on the surface of needle valve to cause the failure of the sealing surface.Particle abrasive wear appears mainly in the early wear phase of needle valve,which produces scratches in the surface,and adhesive wear and a large area of spalling appear in later period.