The cavitation erosion behaviours of the main two steels used in hydroturbine are investigated in distilled water with and without sand by ultrasonic vibration equipment for cavitation erosion. The results show that the resistance of higher hardness 0Cr13Ni5Mo stainless steel to cavitation erosion is superior to that of lower hardness 20SiMn steel. During cavitation erosion in distilled water, the breakaway from 0Cr13Ni5Mo stainless steel is uniform, but that from 20SiMn steel is not, and there are obviousl...