The invention provides a method and a device for applying dimethyl phosphite hydrogen chloride tail gas to synthesis of glyphosate. The method comprises the following steps: conveying dimethyl phosphite tail gas into a compressor through a pipeline, and carrying out primary pressurized condensation to obtain a high-boiling-point alcohol water solution and non-condensable gas; carrying out cryogenic treatment on the non-condensable gas in a secondary pressurized condenser, separating the product to obtain hydrogen chloride gas, and storing the hydrogen chloride gas in a hydrogen chloride gas cabinet; carrying out an acidolysis reaction on the hydrogen chloride gas and the synthesis liquid in a hydrolysis kettle, then carrying out heating desolvation and deacidification and feeding the product into a cooling crystallization process; and then carrying out solid-liquid separation through a washing device, and finally drying the product to obtain the glyphosate raw medicine. According to the method, the hydrogen chloride and the methyl chloride are separated through pressurization and condensation, then the methyl chloride enters a refining procedure, and the separated hydrogen chlorideis applied to the glyphosate production mode, so that the introduction of water in a reaction system can be reduced, the steam consumption during solvent recovery is reduced, and the wastewater amount is reduced. The water for glyphosate production is reduced, the wastewater treatment and energy consumption are reduced at the same time, and the economic and environmental benefits are remarkable.