The invention relates to a carrying disc monitoring system. The system involves a plurality of carrying discs and a reflow soldering machine, wherein the carrying discs are used for carrying and positioning at least one circuit board, and the reflow soldering machine comprises a conveying belt, a processing module and a database; and when one certain carrying disc is arranged on the conveying belt, a plurality of convex blocks which are arranged at the bottom of the carrying disc and are used for identifying different carrying discs press partial sensing units on the conveying belt, each pressed sensing unit is used for transmitting a sensing signal to the processing module, the processing module acquires carrying disc codes according to the sensing signals, the processing module judges which carrying disc is arranged on the conveying belt according to identification codes stored in the database and the carrying disc codes acquired by the processing module, and thus the technical effect of monitoring the carrying discs entering the reflow soldering machine is achieved.