The invention provides a floating type water quality detection device in an aquaculture Internet of Things online monitoring system. The floating type water quality detection device comprises a floating shell, a sealing cover, a port sealing piece, a supporting seat, a solar power generation plate, a storage battery, an integrated circuit board, a detection sensor group and a signal transmitter, wherein the storage battery, the integrated circuit board and the signal transmitter are arranged in the floating shell; the detection sensor group for detecting temperatures, dissolved oxygen and pH (Potential of Hydrogen) values are hermetically mounted at the bottom of the floating shell; the sealing cover is hermetically mounted at the upper port of the floating shell; the lower end face of the supporting seat is fixedly arranged on the sealing cover and the solar power generation plate is mounted on the upper end face of the supporting seat; the solar power generation plate is electrically connected with the storage battery; the storage battery supplies power to the integrated circuit board, the detection sensor group and the signal transmitter. The floating type water quality detection device can be used for carrying out real-time synchronous detection on the water temperatures, the dissolved oxygen and the pH values of a pond; an external electric supply is not needed and an electric wire does not need to be erected in the pond; the floating type water quality detection device is one of key equipment in the aquaculture Internet of Things online monitoring system.