Abstract: Based on the series of experimental studies (I), (II), this test was carried out by using drilling mud as the wording medium to obtain the optimal technical parameters of the rubbing of high-chromium cast iron against perbunan rubber. Six series of tests for the testing rings, which are made of high-chromium cast iron with different hardness and surface finishs, rubbing against the testing blocks, which are made of perbunan rubber with different hardness, were carried out on the dynamic abrasive machine MLD-10. Now more than one thousand data have been obtained, from which matched values between the hardness and surface finish of high-chromium cast iron and the hardness of perbunan rubber are obtained. The effect of the hardness and surface finish of high-chromium cast iron, the hardness of perbunan rubber and working medium, etc. on the wearability of high –chromium cast iron and perbunan rubber has been made clear, so that technical parameters for designing liners and pistons are given out, and some noticeable problems are presented in this paper when they are in use.