In recent years, many efforts have been made to reduce pollution in compression ignition engines. Dimethyl ether is one of the methods to achieve this goal due to its special properties such as high Cetane number and low pollution. Also, one of the parameters that plays an important role in improving combustion and engine performance is fuel injection pressure. In the present study, a numerical study was performed to investigate the performance and pollution characteristics of a compression ignition engine using alternating fuel diesel fuel by changing the fuel injection pressure. In this study, the combustion characteristics of a four-cylinder direct injection diesel engine are simulated with specific physical characteristics with ANSYS Fluent software. Using Dimethyl ether fuel by increasing the fuel injection pressure up to 800 bar, increase in the maximum pressure and decrease in the maximum amount of reaction heat, temperature, nitrogen oxide and soot in Dimethyl ether fuel compared to diesel fuel is about 14 and 7.9, 11.7, 79 and 78.7 percent.