Abstract: The problem of unsteady revolutions of the diesel engine is a complicated one. This paper discusses the problem from the poit of view of vibration theory. In this paper the equation of motion is established and the equation of judgement of steadiness is also developed. According to thess equations, due explainations are given to the reasons for unsteady revolutions, some complex phenomena are analysed theoretically and some methods to control unsteady revolnutions are offered herein This paper is peculiar in discussing the problem of unsteady revolutions of diesel engine, hence it is of great value for reference. It is published here just for further discussions.