Abstract: The existed trouble is that the one capacitor system with time-delay are difficult to control usually in industrial control field.The aim of optimal control for a pure time-delay system is to form a robust-control system with short step response time based on the method of twice optimum control(TOC).The optimal robust control method of a pure time-delay system is presented under the evaluation standard of integral time and absolute value of error(ITAE).This method involves two stages,i.e.time-dividing model choice and parameters optimizing.The corresponding optimal algorithm is given.The clone and chaos technology is used to optimize parameter.At last,the comparison results of system response for optimal parameter is given.The experimental results show that this optimal control method is efficient and accurate.