Abstract: This paper focuses on the analysis of machine cutting on some FF-NL level valves used in wellheads in Sichuan and Chongqing gas field.Through analysis it is found out that the fluid medium channel, composed of valve, valve plate and valve base, is in corrosive and gas-liquid multiphase environment with high temperature, high pressure and high velocity, and the inner surface of the channel tends to be influenced by both of electrochemical and mechanical impact-corrosion, so the erosion and pitting corrosion relatively stand out.Because of the difference in material selection, valve rod and valve plate show the feature of galvanic corrosion and sealing failure.While in corrosive environment, bearing assemblies tend to show stress-induced corrosion.Furthermore, the binding face between valve base and body is qualified for crevice corrosion.The indoor results of simulated corrosion indicate that the main material 12Cr13 of valve has more severe corrosion in simulated working condition.After forming the galvanic couple by 12Cr13 and 718 nickel base alloy, the corrosion rate increases obviously.