The oxidation behavior of high speed steel (HSS) was researched by high temperature thermo balance at 500 to 800 °C in water vapor. The morphology was observed by scanning electron microscope, the microstructure of oxide scale was analyzed by energy dispersive spectrometer and X-ray diffraction spectrum. The results indicate that the mass gain of HSS increases with oxidation temperature rising, the effect of oxidation temperature on the morphology is obvious, water vapor temperature only affects mass gain and affects hardly morphology of oxide scale at the same oxidation temperature. The relevant oxidation mechanisms are also discussed. The oxidation behavior of high speed steel (HSS) was developed by high temperature thermo balance at 500 to 800 ° C in water vapor. The morphology was observed by scanning electron microscope, the microstructure of oxide scale was analyzed by energy dispersive spectrometer and X- The results indicate that the mass gain of HSS increases with oxidation temperature rising, the effect of oxidation temperature on the morphology is obvious, water vapor temperature only affects mass gain and storage hardly morphology of oxide scale at the same oxidation temperature. The relevant oxidation mechanisms are also discussed.