The high temperature oxidation resistance property of Y+ implanted H13 steel has been studied by 5.8 MeV proton backscattering. The measured oxygen area density of H13 steel after implanted with Y+ and oxidized at 800℃ for 45min shows that the oxidation speed is decreased by a factor of 25. The experimental results also show that for Y+ implanted H13 steel an enriched Cr layer was created and the behaviour of oxygen diffusion is apparently different from that of unimplanted samples.