Abstract: Diethyl carbonate(DEC) synthesis reaction by oxidative carbonylation of ethanol has been studied using vapor phase flow reaction system in the presence of Cubased catalyst prepared by the conventional impregnation method. The effect of various preparation parameters on the catalytic activities were intensively evaluated in terms of ethanol conversion and DEC selectivity. The results show that activated carbon and CuCl2 are better support and precursor respectively and their catalytic activity was improved when Pd(PPh3)2Cl2 was applied as the promoter. The catalyst had better activity when Cu and Pd loading are 9.0% and 0.5% respectively. The conversion of ethanol was over 30% and DEC selectivity was 95% under optimum preparation condition and the catalysts retained better catalytic activity in 100h continues reaction.