Abstract: Water quality detection is important for intensive deep-sea aquaculture, and water quality affects fish growth directly. At present, the main ways of water quality detection is to build a water quality monitoring network system and manpower collection of water samples for detection, which are complicated and inefficient, with limited operation area, long monitoring cycle and other problems. Thus, this paper designed an operational underwater robot for water quality detection on aquaculture ships. Firstly, the overall design of water quality detection system and underwater robot system was proposed. Then the mechanical structure of underwater robot was designed by modelling software Solidworks. The housing adopted a streamlined structural design, and was equipped with pumping hose port. The design of two horizontal and four vertical propellers is to ensure that the underwater robot can move freely. Based on the Ansys software, stress numerical simulation was conducted on the housing, fixed structure as well as pressure chamber of the robot, and theoretical calculations were combined to improve the robot design. The results show that the underwater robot's sealing, degree of freedom, pumping detection and other performance tests meet the working requirements, and can reach the designated location for stratified and fixed-point water quality sampling; the obtained water quality detection data can provide data references for aquaculture.