The combustion process of diesel engine was influenced by the parameters such as injection times, injection timing, injection amount, injection pressure and EGR rate. The high frequency pressure oscillation inside cylinder during combustion was strongly correlated with the combustion noise. Nine sound level meters were placed in different locations surrounding diesel engine and the average sound intensity level and spectrum characteristics were analyzed so as to study the influence of pilot injection strategy and EGR on the noise of 4cylinder highpressure common rail diesel engine. The test results show that pilot injection will worsen engine noise at low load with a little fuel injection amount per cycle. A small amount of pilot fuel injection can shorten the ignition delay period and hence achieve the reduction of noise, but more of pilot fuel injection will not benefit the noise reduction at high load with a high fuel injection per cycle. Delaying main injection timing appropriately can reduce the sound pressure level of the peak frequency range corresponding with main combustion. Advancing pilot injection timing will increase the sound pressure level in the frequency band of pilot combustion and dual peaks of sound pressure level can be seen on the spectrogram. In addition, increasing the opening rate of EGR appropriately can reduce the engine noise.