A method of controlling combustion of a diesel engine may include a vibration measuring step of measuring engine vibrations, a measurement region setting step of setting a range where an LPP (location of peak pressure) is predicted from measured vibration data, a frequency transforming step of transforming a vibration signal to a frequency response function, a frequency integrating step of integrating the transformed frequency response function, an LPP detecting step of selecting a location of peak pressure from integrated frequency response function, an estimated value determining step of selecting LPP offset and SOC (start of combustion) offset by using the detected LPP, an error determining step of determining LPP value error and SOC value error by comparing the estimated LPP value and the estimated SOC value with a target LPP value and a target SOC value, and a combustion correcting step of correcting and controlling combustion by the determined errors.