This paper investigated the working mechanism of a new type of graphene based nanofluids in turning Ti-6Al-4 V. Comparative study was conducted to analyse chip formation, cutting temperature and surface roughness in turning Ti-6Al-4 V with graphene oxide (GO) nanofluids. Surface topography and chip morphology were examined when turning with polycrystalline cubic boron nitride (PCBN) inserts by scanning electron microscope (SEM). Influences of coolant pressure, concentration and machining parameters such as cutting speed, feed rate and cutting depth were investigated. The results showed that the surface roughness was reduced by about 34.34% when using GO nanofluids as compared with conventional coolant. The cutting temperature was reduced by 27.16℃, 30.42℃, and 31.8℃, respectively when lower velocity, lower feed and higher coolant pressure were applied whereas the cutting temperature decreased by 50.53℃ when the pressure of the GO nanofluids was 10 bar.