Abstract: Friction and wear behavior of CrNiMo steel against H96 brass in different atmospheres like oxygen and carbon dioxide were investigated on the MMS-1G tribometer under high speed and dry sliding. Contact surface temperature of pin was measured by NiCr-NiSi thermo-couple inserted into the hole of the CrNiMo steel pins. The morphologies of the worn surface were observed and analyzed by scanning electron microscopy and X-ray photoelectron spectroscopy. Influences of pv value on tribological behavior were investigated in different atmospheres. The results indicate that, friction coefficient and wear rate of CrNiMo steel in carbon dioxide atmosphere were higher than that in oxygen atmosphere due to the difference between the contact surface temperature and wear mechanisms in two kind of atmospheres. The wear mechanisms of CrNiMo steel were mainly abrasive wear, metal flow and adhesive wear in the carbon dioxide atmosphere, and in oxygen atmosphere the wear mechanisms were mainly oxidative wear and adhesive wear.