Titanium alloy is a typical hard-to-machine metal and a lot of serrated chips are often formed in the cutting process. The appearance of serrated chips will not only cause the fluctuation of cutting force, resulting in the decline of cutting accuracy, but also lead to the rapid wear of tools. In this study, the formation mechanism of serrated chip of Ti-6Al-4V titanium alloy was investigated by a two-dimensional cutting simulation model of Ti-6Al-4V titanium alloy, which was established by using the Johnson-Cook constitutive model and Johnson-Cook fracture model. It is found that shear slip occurs with the decrease of the shear band and the overall stress during the formation of serrated chips. The peak temperature is reached at the end of the shear band. Meanwhile, the "dead zone" of temperature and stress is formed near the edge of the tool, which has an obvious periodic alternating trend in the cutting process, resulting in the macro curl and micro serration of chips.