This paper introduces the cycle-to-cycle variation study under various operating conditions on direct injection type diesel engine 2135 and swirl combustion chamber type engine S195 using pure diesel fuel, water emulsion and additives. The cycle-to-cycle variation is expressed by three parameters Pmax, pi and Tmax in these experiments. And the standard deviations of these parameters are evaluated, the histogram of probability distribution of their deviation is applied. In this paper, the degree of influences and the law of variations of every parameter are analyzed in detail, some specific data of variations are offered; thereby explicit conclusions are obtained.