A deep understanding of the generation and characteristics of serrated chip formation can obtain some practical advices of controlling this type chip in engineering applications. The characteristics of serrated chip including the frequency of serration, the degree of segmentation and the space of adiabatic shear band are comprehensively investigated in this paper. Experiments of high speed milling Ti6Al4V were performed. The investigated material is Ti6Al4V since it is prone to form serrated chip in machining process. The chips of Ti6Al4V under different cutting speeds and feed per tooth were collected during machining. After inlay and polishing process for the collected chips, the chip morphology could be observed by VHX 600 ESO digital microscope. The expressions of the frequency of serration, the degree of segmentation and the space of adiabatic shear band were determined through microcosmic observation. The results show that the space of adiabatic shear band gets decreased with the increase of cutting speed and the feed per tooth. On the contrary, the frequency of serration will get increased with the increase of the cutting speed and it will get decreased with the increase of the feed per tooth. The increase of cutting speed or the feed per tooth could intensify the degree of chip segmentation. The degree of segmentation can be used as the criterion of ordinary cutting, high speed cutting and ultra high speed cutting.