In view of how to realize underwater patrol, underwater operation and so on, this paper introduces a patrol robot which can monitor the water environment in real time and operate in underwater. Use hemispheric hood and three-compartment structure design. The modular design is divided into control module, power module, detection module, navigation module and underwater operation module, and verified by experiment. The experimental results show that the robot has the advantages of practicality, simple operation, stable navigation, strong maneuverability, easy to carry and recycling.