The invention discloses an energy saving and environment-friendly technology for co-producing fuel grade and refined dimethyl ether by dehydrating methanol which belongs to the field of new energy, chemical industry and catalysis. The technology essentially consists of methanol vaporization, catalytic reaction, double-tower rectification and methanol-water separation. The technology is characterized in that a solid acid catalyst with good low-temperature activity is used during the process of catalytic synthesis; a component fluidized bed or an isothermal multitubular fixed bed reactor which is easy for controlling the reaction temperature is used during the catalytic synthesis; the reaction heat during the process of methanol dehydration is used completely; the reflux ratio of a dimethylether pre-rectifying tower and a dimethyl ether rectifying tower and the extraction ratio of the tower top and a lateral line are adjusted to realize fuel grade dimethyl ether and chemical industrialgrade dimethyl ether in different output proportions; the invention uses fully-closed rectification to avoid the discharge of purge gas; a methanol rectifying tower is operated by micropressure for draining under the pressure difference; and the waste water can reach the national emission standard and is safe and environment friendly.