The invention discloses an automatic control method of a duplex decarburization converter, belonging to the technical field of automatic control of converter steel making. According to the invention, based on a present related two-level system, a dynamic event-triggered mode is designed which comprises an oxygen demand absolute value event, a relative main blowing ending oxygen demand event, a relative blowing ending event, a relative deslagging accomplishing event, and a percentage event, and the original fixed mode relative to oxygen demand percentage is replaced; simultaneously, a mode that an oxygen lance and charging mode automatically carries out pattern matching according to Si content of the filled molten iron, Mn content of the molten iron, and the temperature of the molten iron;according to the actual situation of the semisteel, the two-level system automatically selects corresponding mode data, and distributes corresponding control data to the primary PLC system to finish the automatic control of the whole blowing process. The invention has the advantages of improving the automatic control level of the duplex decarburization converter, and simultaneously improving the double hit rate of the converter blowing terminal point.