This paper describes the investigation of the mechanisms of engine front noise generation and the corresponding countermeasures employed in the development of a diesel engine. According to the analysis of acoustic signals and vibration signals measurement, an investigation of the noise source identification in a diesel engine is presented, and that the noise level of the diesel is comprehended. With the sound intensity method, the major sources of the exterior radiation noise of the engine front are surveyed. The research provides the reliable basis for the engineering practice to reduce vehicle noise level. Furthermore, the measuring data of the acoustic signals are compared by measuring noise from surface vibration, and the results are valid.