Abstract: By measuring the topographies of inner surfaces of diesel cylinders, the author carried out a study on the current running-in specifications of Dongfeng 4B diesel locomotive engine through simulation tests. In the tests, after analyzing the state parameters in the running-in process, the author proposed a new test procedure, modified running-in specifications, for the running-in process of cylinders. The new specifications proposed was applied to the running-in test on a practical locomotive diesel engine, and the difference between the topographies of the inner surface of a cylinder was analyzed before and after the running process to estimate the effect of the new procedure. The results show that the running-in time with the new procedure is about 37% shorter than that of the current running-in specifications.