The invention discloses a method and a device for synthesizing chloromethyl ethyl ether, an immediate of acetochlor. Polyformaldehyde and alcohol with the needed amount are added into an A kettle and a B kettle; through circulating ejection systems of the A kettle and the B kettle, hydrochloric acid gas enters the A kettle to react, escaped hydrochloric acid gas continues to be etherified in an ejector of the A kettle and the A kettle, and the unreacted hydrochloric acid gas enters an ejector of the B kettle and the B kettle and continues to react; and uncondensed gas enters a condenser and an absorbing tank. When a product in the A kettle is qualified, the product is discharged; the operation is switched to feed fillings into the A kettle; the hydrochloric acid gas enters the B kettle for etherification, the escaped hydrochloric acid gas continues to be etherified in the B kettle and the ejector of the B kettle, the unreacted hydrochloric acid gas enters the A kettle and the ejector of the A kettle and continues to react, and unreacted light component gas enters the condenser and the absorbing tank; when a product in the B kettle is qualified, the product is discharged, and one-time switching operation of the A kettle and the B kettle is finished. The utilization rate of the hydrochloric acid gas is improved by 30 percent or so, no waste water exists during the etherification, and the cost of the product is apparently reduced.