Abstract: The high temperature friction and wear characteristics of two kinds of hot work die steel（4Cr5MoSiV and H13） were studied on UMT-3 high temperature friction and wear tester. The morphological characteristics and phases of wear surface and cross section were analyzed by X-ray diffractometer（XRD）, three-dimensional optical profilometer, scanning electron microscope（SEM） and metallographic microscope. The test results show that compared with traditional H13 steel,4Cr5MoSiV has lower friction coefficient, better lubricity and better wear resistance. The friction coefficient of the two kinds of hot work die steel（4Cr5MoSiV and H13） treated with nitriding is lower than that of the non-nitriding steel, which is reduced by 7.7% and 5.9%, respectively, and the wear resistance is increased by 10.2% and 23.0%, respectively. The microstructure after nitridation has clearer grain boundaries, coarser grains and higher microhardness than that without nitridation. The nitridation of 4Cr5MoSiV and H13 steels has improved by 108% and 105% respectively. Fatigue and severe oxidative wear are the main wear mechanisms of the two kinds of hot work die steels treated without nitriding. The main wear mechanism of4Cr5MoSiV treated with nitriding is slight oxidative wear and small abrasive wear in the test temperature range. The main wear mechanism of H13 steel treated with nitriding is oxidative wear and abrasive wear.