Abstract: Mud pump liner is the key parts of oil development equipment. Because of the severe operating conditions, its service life is very short. With high-chromium cast iron used for liner, its life may increase significantly, but the mineral resources of our country are short of chromium. This paper analyzes ten high- chromium cast iron liners serviced and worn out in different region, it involves mettallographic analysis of worn-out surfaces, analysis of surface topographies by scanning electron microscope and wear debris analysis. By discussing the failure process and essential wear mechanism, some new conceptions of theoretical and practical significance are presented. It is pointed out that the wear out of martensitic matrix of high-chromium cast iron results in break and collapse of convex carbides owing to lossing support. As a result of collapse of carbides, matrix losses support and falles in rapid wear out. When carbides appear again on the working surface, the matrix comes into slow wear out. Then, matrix wear out, convex carbides appear, break and collapse, and new rapid wear out results. Because of this repeated process, the high-chromium cast iron liner wears out unceasingly and failure at last. It may be concluded that the essential failure mechanism of high-chromium cast iron liner is owing to break and collapse of carbides. Based on the results of material-matching tests, it is pointed out that the best chromium content is about 10%, by which it is not only ensuring the good wear-resistance, but also reducing cost by 17. 85% from the decreased chromium content. The new model liner, manufactured according to the data of this paper, has been efficiently used in South west-Sichuan Oil Field.