With regard to the situation that the existing iron roughneck requires manual assistance when detecting the center and processing interface of drill pipes to fulfill the drill pipe processing operation, we develop the drill pipe processing interface auto-detective system. This system consists of a linear displacement sensor， 300 PLC controller and a linkage mechanism which can reset automatically. This system not only achieves the full-automatic detection of the drill pipe center, also detects the interface of drill pipes automatically. This eliminates the manual operation step during the drill pipe operation and improves the automation level of iron roughneck.