Abstract: Hook type of oscillation mark was the primary problem about surface quality of strand which was used to product 35K cold Forging steel.The reason that induced hook type of oscillation mark was the poor lubrication of mould flux.On one hand, hook type of oscillation mark would make surface defects on strand, such as inclusion, crack and hypodermal pore.On the other hand, it would produce the phenomenon of nonuniform microstructure because of the poor heat transfer which induced huge austenite grain and developmental microstructure on the surface of strand.It finally caused crack of cold forging steel.Therefore, through optimizing capability about physical property and chemical composition of mould flux and improving the lubrication capability of flux, the hook type of oscillation mark had been removed and the nonuniform microstructure phenomenon on oscillation mark had been controlled.In the end, it provided eligible strand for subsequent rolling process.