A hydraulic control system of oli tank cleaning robot was designed to afford the operating safety and flexibility.Firstly,all component elements of the hydraulic control system were confirmed after analyzing the structural characteristics and functions of the robots.Secondly,on the basis of working principle and process of every component element,a hydraulic system circuit was designed for the robot and the achieving process of every component element was analyzed.Last,the PLC control system and the electro-hydraulic servo control system were respectively devised.On the basis of transfer functions of all component elements,the whole transfer function of the system was built.It provides a theoretical foundation for component element selecting and circuit simulation.