Abstract: The wear failure of the gas valve/valve seat in engine has been investigated with a simulating tester. The wear mechanisms of the valve seat have been examined based on the observation of the worn surface morphologies of the valve seat by means of scanning electron microscopy. As the results, the failure of the contact surface of gas valve/valve seat is characteristic of elastic/plastic deformation and fatigue cracking and spalling. The creep sliding and atmospheric corrosion enhance the wear of the valve seat at high temperature.