The invention relates to an auxiliary control device for a fish tank. The auxiliary control device is mainly characterized by comprising a power supplying unit, a card type computer, a single board computer control module, a WIFI router, a 3G module, an LCD display screen, a webcam, a direct current motor control module, a switch control module, a transducer time division multiplexing controller and a transducer set. The card type computer is connected with the single board computer control module connected with the transducer set through the transducer time division multiplexing controller; the card type computer is further connected with the WIFI router, the 3G module, the LCD display screen and the webcam; the single board computer control module is further connected with the direct current motor control module and the switch control module. The auxiliary control device for the fish tank is reasonable in design and is connected with the internet through the WIFI/3G module and a home use wireless AP. The state of the fish tank and the state of fishes in the fish tank can be managed by a cell phone client in real time, so that a remote monitoring function on the fish tank is achieved. The auxiliary control device for the fish tank can be widely applied to the visible ornamental fish tank and cultured fish industries including home furnishing, shops, ornamental fish wholesale markets and the like.