Abstract: An SRV friction and wear tester was performed to evaluate the wear behavior of graphite IG-11 used in 10MW high temperature gas-cooled reactor (HTR-10) in sliding against graphite and stainless steel at ambient temperature in air and helium. The worn surfaces of the upper graphite samples sliding against the graphite and stainless lower counterpart were observed using a scanning electron microscope. It was found that the wear behavior of the graphite was closely to the gas environment as it slid against the graphite counterpart. Contrary to the above, the effect of the gas environment on the wear behavior of the graphite became insignificant as it slid against the stainless steel counterpart. This was because the plowing of the graphite by the hard stainless asperity played a dominant role for the graphite-stainless steel pair. At the same time, the differences in the wear resistance and worn surface features of the graphite samples in different gas environments conformed to the differences in the shape and size of the corresponding wear debris. Namely, the graphite sample was dominated by abrasive wear in helium environment, which corresponded to a large wear rate of the graphite and small size of the wear debris. While in air environment, the graphite was characterized by fatigue wear, which corresponded to a small wear rate of the graphite and large size of the wear debris as compared in helium.