The invention belongs to the technical field of chemical industry production, and relates to a device used for lowering the acid value of a TDI product produced through a heavy solvent method. A feeding preheater is connected to the middle of a product tower in a butt mode through pipeline communication to preheat photochemical reaction materials, the top of the product tower is connected with a product tower condenser used for condensing and recycling the TDI product, a reboiler arranged at the bottom of the product tower in a communication mode is used for vaporization backflow, the bottom of the product tower is in pipe communication with a purging tower through a residue pump so as to purge acid components conveniently, and the reboiler, the residue pump and the purging tower are in pipe connection and communication. The top of the purging tower is connected with a purging tower condenser used for condensing and recycling acid components. Distribution devices of spray structures arranged in inner cavities at the top and bottom of the purging tower are used for distributing heavy solvent isophthalic acid diethyl ester and inert gas. All the devices are provided with pipelines and ports thereof for conveying materials. The whole device is scientific in design, reasonable in structure, easy to operate, convenient to use and good in application environment.