Cavitaion erosion behavior of cast iron in water and in mixed solution of 50% H2O+50% C2H6O2 with different temperature and distance between two samples have been studied by means of a ultrasonic vibrator. The mass loss of the samples at different time is recorded.The surface structure of the oxidation films on the surface of cast iron was analyzed by X-ray diffraction apparatus. The experimental results show that mass loss of the upper sample is more than that of the lower sample. The maximum of mass loss occurred when the distance between the samples is about 1.0mm. Oxidation films form on the surface of the cast iron in pure water and cannot form on the surface of cast iron in mixed solution. The XRD results show that the oxidation film mainly consists of Fe2O3 phase at 50°C, Fe3O4 phase at 80°C. The mass loss at 50°C is less than that at 80°C. Oxidation film of Fe2O3 phase has some advantages to decelerate the cavitation erosion. Mass loss of the sample of cast iron in mixed solution is less than that in pure water at 80°C. This phenomenon indicates that formation of the oxidation films plays a more important role in cavitation erosion to reduce or increase mass loss of the cast iron samples.