This paper presents three factors of operating efficiency， cognitive load and naturalness when designing the human computer interface of an energy management system（EMS）. The former two factors have always been the design standards while naturalness is the new factor to meet the current computer technologies. According to the three factors， this paper proposes six design rules based on the research of the input-side. These rules demand balancing the three factors and providing a satisfying input environment， and improving the entire input ability of human computer interface by coordinating the input tools and the use of the new algorithm.