Cylinder pressure level is defined the value of sound pressure level derived from relations of pressure and frequency which are obtained Fourier series expansion of cylinder pressure. CPL is alone in general use in combustion analysis without regarding attenuation coefficient determined by engine structure because it is almost constant in various kinds of engines. Combustion pressure fluctuation and influence of CPL was investigated in this paper using Wiebe combustion function superposition th obtain the effect of premixed and diffusive combustion. The results are as follow. (1) Influence of combustion maximum pressure(P$sub$max/) on CPL is correspond with total energy per cycle well. (2) P$sub$max/, .DELTA.P$sub$max/, (dp/d.theta.)$sub$max/ and (d$^$2/p/d.theta.$^$2/)$sub$max/ are very effective on CPL in the range of low frequency, mid-low frequency, mid-high frequency and high frequency respectively.