It is known that diamond-like carbon (DLC, a-C:H) coatings show low friction and high wear resistance under inert gas environment. However, hydrogen-free DLC (a-C) coatings show relatively high friction under such environment. And, both a-C coatings and a-C:H coatings can not achieve relatively low friction coefficient. So, super-low friction of a-C coatings and a-C:H coatings under humid N_2 gas environment is achieved in this study by introducing running-in period and controlling relative humidity. We conduct friction tests of a-C coatings, a-C:H coatings under various humid environment. When contacts between each coatings are maintained respectively and we increase relative humidity (4.2-40 %RH, 0.7-40 %RH), value of friction coefficients are 0.021 and 0.027 respectively and independent of relative humidity. It is considered that humid is a key of super-low friction of carbon based hard coatings.