The effects of temperature, pressure, and the initial composition of feed gas on the synthesis of dimethyl ether from CO hydrogenation and from CO2 hydrogenation are investigated in a wide range of reaction conditions. By the detailed contrast between the dimethyl ether synthesis process from CO hydrogenation and that from CO2 hydrogenation, it is seen that the former holds an advantage over the latter because of outstanding synergic effects. On the basis of the observation of the transition processes by adding CO2 into the CO hydrogenation system through two different ways, it has been found that there are two kinds of critical states in which the equilibrium conversions of CO and CO2 reach zero. After many critical states in the whole triangle region composed of the feed concentrations Of CO, CO2, and H-2 are obtained, the dimethyl ether synthesis process is divided into three parts: CO hydrogenation, CO2 hydrogenation, and parallel hydrogenation of CO and CO2.