Interactive Drama is a drama which is created by user\'s participation in virtual environment. In this world, user can interact with characters and user\'s play affects the story. The purpose of this study is analyzing existing interactive dramas and finding problems. The analysis based on theory of Aristoteles and Brenda Laurel. The facts which have influence on dramatic experience are: story, interactivity, usefulness. First of all, story of drama has dramatic arc, diversity of story, natural inducement of user\' participation and twist ending. Interactivity is related to range, frequency, significance and diversity of character\'s reaction. Easiness of use and possibility of save support usefulness. The result of this study lets us know that existing interactive drama, MIMESIS, IDtension, I-Storytelling, Façade are hard to generate twist ending. To solve that problem, we try to improve the HTN Tree and Beat Management system, and show the examples of story.