Diesel engines in both automotive and industrial types are one of the most efficient engines in the world. Improving emissions and reducing fuel consumption is of great importance in the automotive industry. There are various methods in order to reduce emissions and fuel consumption of diesel engines. In this paper, at first it is tried to use the common rail fuel injection system to provide high pressure fuel behind the injectors and improve combustion inside the combustion chamber. It will decrease, soot, HC and CO emissions and fuel consumption while maintaining the performance of the OM355 diesel engine. It should be noted that by using the common rail system and better evaporation of fuel by the injection system and increasing the combustion efficiency, while reducing soot, HC and CO, the amount of NOX also increases. Therefore, after this stage, using a system to reduce the amount of NOX is necessary to create a trade-off between soot, HC, CO and NOX. So, with the use of Selective catalytic reduction (SCR) catalyst, which is one of the efficient technologies for controlling and reducing NOX, the amount of NOX in the post-combustion phase is significantly reduced. The experimental results of the OM355 engine test show the proper operation of the common rail and SCR systems.