This paper describes a computer method for power system planning. Power system planning was usually studied through individual programs. Because of the laborious work involved in data preparation, the increase of task for power system planning and the time required for the detailed analysis of results, the available time for assessment and decision making has been sacrificed. In order to improve the above situation, the use of data base techniques an the simplified evaluation of the presented programs were newly developed. This program has been used successfully for the routine of power system planning in Korea Electric Company. In addition, this paper describes some results of analysis and evaluation of power system planning in KECO.