The invention relates to a high-pressure continuous reaction system for producing 3,6-dichlorosalicylic acid, and belongs to the technical field of an intermediate of a synthetic herbicide dicamba. The system comprises a batching kettle, a carbon dioxide absorption kettle, a high-pressure reaction section and a pressure-relief discharge section which are sequentially connected; the high-pressure reaction section comprises a reaction pipeline and a mixer arranged on the reaction pipeline; the pressure-relief discharge section comprises a pressure-relief valve, a buffer tank, a condenser, an acidification kettle and a filter pressing device which are sequentially connected. By the system, the 3,6-dichlorosalicylic acid can be efficiently and continuously produced.