TiN coatings with 0–8 vol.% CO addition were prepared by chemical vapor deposition at 1000 °C. Pure TiOCN phase was formed with different CO additions, and no apparent local elemental segregation was found. With increasing CO content up to 6 vol.%, the dissolution of O and C increased, accompanied by a decrease in N content and a reduction in grain size. Further increasing the CO content to 8 vol.% did not result in any apparent changes in the amount of O/C dissolution and coating grain size. The intensity of [111] orientation was the highest with 2 vol.% CO addition. The adhesion strength decreased as the CO addition increased, while the hardness first significantly increased with 2 vol.% CO addition, and then remained nearly constant with further increasing CO addition up to 8 vol.%. As the CO content increased to 8 vol.%, the insert continuous cutting life of machining QT500 spheroidal graphite cast iron exhibited a trend similar to that of the hardness.