The premixed diesel combustion is effective for the high thermal efficiency and the reduction of NOx and PM emissions, but the reduction of combustion noise is necessary at medium-high load operation. The control of the fuel injection becomes more accurate than previous because of the technical progress of the common rail fuel injection systems, and the target heat release phase, calculated by computation, can be achieved by the controls of EGR, boosting, injection timing, and injection quantity of multiple fuel injections. In this paper, the reduction of premixed diesel combustion noise with keeping high thermal efficiency has been investigated by the control of multiple fuel injections. The research was approached from both the engine simulations and the experiments. In the combustion noise simulation, the heat release histories of multiple injection were approximated by the Wiebe function, the simulated combustion noise was calculated from the fitted curves of the heat release and the coherence transfer function, as a result the effects of the heat release history on combustion noise and indicated thermal efficiency could be further investigated. The structural attenuation of test engine was calculated from the power spectrum of the FFT analysis of the in-cylinder pressure wave data and the cross power spectrum of the sound pressure of the engine noise by the coherence method. The supposed engine speed and load in the simulation were 2000 rpm and 0.7MPa respectively, the fuel was injected three times near the TDC and the parameter variables are the injection times and duration between the heat releases. Then, the simulation results were fed back to the engine tests, a supercharged single cylinder DI diesel engine, and the accuracy of the simulations were verified. The results showed that the multiple injections with the similar maximum pressure rises at TDC is effective to the high thermal efficiency with low engine noise, because of the high degree of constant volume and noise cancelling spike combustion effects.