Abstract: The influences of cooling EGR temperature on the emission of Nitrogen Oxide, Hydrocarbon, Carbon Oxide, smoke intensity and fuel consumption rate through the test of procedure were studied, in order to get the influence on emission performance of the diesel engines by cooling EGR. Based on the above, the best EGR temperature under various operating modes of diesel engines was obtained. The experiment indicated that compared with hot EGR, the cooling EGR could reduce the emission of Nitrogen Oxide and smoke intensity obviously, and also can reduce the fuel consumption rate and improve the efficiency of diesel engines, and the effect obtained is better.