This paper deals with the combustion chamber shape effects on in-cylinder air motion and performance of a DI diesel engine. Three different shapes of diesel engine combustion chamber are selected and simulated by means of multidimensional modeling technique. The turbulence, squish and turbulence energy in cylinder are systemically analyzed. To validate the numerical model, experimental study is made on a single cylinder DI diesel engine. The results show that, by optimizing the combustion chamber shape, the duration of high turbulence in cylinder is prolonged, and the diffuse combustion during the later period of combustion process is enhanced. Therefore a good trade-off of NOx, smoke and fuel consumption is achieved by retardation of fuel injection.