ABSTRACMany studies on the Cyclic variation of combustion process are made with a spark ignition engine. However, there are scarcely such studies with a diesel engine. Because, in general, the combustion of diesel engine is believed very stable. However, there exist some combustion variations in a diesel engine. As it is universally known, the combustion in a diesel engineis the series of a pre-mixed and a diffusion combustion, which is completely different from the combustion of a spark ignition engine. Therefore, it is impossible to determine the combustion variation of diesel engine by a direct application of the results of spark ignition engine. In this report, we discuss the several factors which indicate the combustion variation with a pre-chamber type diesel engine. The maximum pressure Pmax, the maximum rate of pressure rise (dP/dθ )max, the combustion pressure at each crank angle, etc. are analyzed from the continuous five handred of combustion pressure histories statistically. The several engine speeds, loads, compression ratios, charging air rates, exhaust gas re-circulation rates, injection pressures, and fuel temperatures were selected as the engine operating parameters.The results are summarized as follows: (1)The most suitable parameter, which shows the stability of the compression ignition engine, is the variation coefficient of the maximum rate of pressure rise, V[(dP/dθ ) max].(2) The more the load and injection pressure increases, the more the V[(dP/dθ ) max] increases. And the more the engine speed and the compression ratio decreases, the more the V[ dP/dθ )max] decreases. (3) The another parameters are the S[Pmax] and V[Pmax] : the standard deviation of Pmax and the variation coefficient of Pmax. The engine speed, exhaust gas recirculation rate and intake air flow rate do not change the S [Pmax] and V[Pmax]. However, The more the injection pressure, compression ratio and fuel temperature increases, The more S[Pmax] and V[Pmax] decrease.(4) There are one-to-one correspondence between [Pmax] and [Pmax], [Pmax] and [ ( dP/dθ) max], and [ θ [ (dP/dθ )max] and [(dP/dθ max] respectively.