An amphibious robot for in-service inspection of drainage pipelines and a control method thereof are provided. The robot includes a robot body, a detection module for detecting environmental state and pose information of robot itself, a propulsion module including a car-like propulsion module and a ship-like propulsion module for controlling robot movement, a structure conversion module for realizing the conversion between the two modes, a ground terminal controller for remote information monitoring and issuing instructions, a mobile terminal controller for receiving instructions and controlling robot movement and structure conversion, and a power module. The control method includes displaying data through the ground terminal controller, processing environmental information collected by the detection module, determining the robot's working mode and switching working mode through the structure conversion module, adopting the ship-like working mode in deep water, and adopting the car-like working mode in the waterless or shallow water environment.