The Deep Cryogenic Treatment(DCT) process of W4Mo3Cr4VSi HSS was studied by orthogonal experiment method. The paper analysed the effect of various DCT process parameters on mechanical properties and observed microstructure before and after DCT treatment by the SEM. The results show that the effect of soaking temperature on the properties of drill is the first factor, the soaking time is second and the cooling rate is third. DCT enhances the transformation of austenite to martensite, and distributable carbide particles are precipitated from martensite. Therefore DCT increase hardness and enhance wear resistance of twist drill.