The synthesis of dimethyl carbonate (DMC) from ethylene oxide (EO), methanol, and carbon dioxide was investigated. In the proposed one-pot synthesis of DMC, the reaction of EO with CO2 was coupled simultaneously with the reaction of ethylene carbonate with methanol under reaction conditions at which carbon dioxide was in supercritical state. The catalysts were experimentally screened at temperatures from 80 to 140 degreesC and pressures from 5.0 to 15.0 MPa. The mixture of KI and K2CO3 showed the highest catalytic activity for the one-pot DMC synthesis. The preferential weight ratio of KI to K2CO3 in the mixed catalyst ranges from 1:3 to 5:3. The effects of the reaction conditions, such as catalyst concentration, temperature, pressure, reaction time, and reactant compositions, were experimentally studied. High temperature favors the formation of the desired products, DMC and ethylene carbonate. The effect of pressure on the DMC yield is not significant. A high EO content in the feed is beneficial to increasing the selectivity of the desired products. Using the mixture of KI and K2CO3 (weight ratio of KI/K2CO3 = 1:1) as the catalyst with a molar ratio of catalyst to EO of 0.05, the DMC selectivity can reach above 73.0% at 100.0% EO conversion with less than 4.0% selectivity of the byproduct 2-methoxyethanol at the appropriate reaction conditions.