High temperature pin-on-disk tester heated by middle frequency induction was designed. Friction test of hot work die steels with the same composition treated under three different heat treatment conditions was carried out by the pin-on-disk tester at high temperature. The experimental temperature were 200 degrees C, 300 degrees C, 400 degrees C, 500 degrees C, applied loads were 1 kg, 1.5kg, 2kg, 2.5kg, respectively, pin-on-disk circumrotating speed was 1000r/min for all the experiments. Morphology of worn surface and sub-surface structure were observed by optical microscope. Experimental results indicat that wear loss decrease with temperature increasing. Meanwhile, there are various growing rule under different loads, wear loss increase slightly under low load, but increase rapidly with load increasing, especially increment become larger at low temperature. Morphology of worn surface show that the two-body abrasive wear are mainly mechanism under low temperature and low load condition, oxidation wear and adherence abrasive wear are mainly mechanism under high temperature and high load condition.