Thin Cr/C film was synthesized on 4Cr10Si2Mo steel substrates by Plasma Immersion Ion Implantation and Deposition (PIIID). The high-temperature oxidation behavior of Cr/C Coating at 900°C for 100 hours in air atmosphere was investigated. The results show that the Cr/C coating on 4Cr10Si2Mo steel by PIIID process has excellent high-temperature resistance and antioxidant properties. After the oxidation behavior for 100 hours, the surface of coated specimen maintains completely and the Cr/C coating has a good bonding force with substrates. The composition of the oxidation scale and the surface morphology were studied by using XRD and SEM. An uncoated sample and a hard chromium plating sample with same substrate took part in the experiment in same condition for comparing.