This paper proposes a novel planning method for computer generated forces (CGFs) in war games that plans the behaviors of CGFs according to a given mission and situations. CGFs which are received their missions first plan their tasks for accomplishing the mission and then plan their behaviors for accomplishing each task. After that, they execute their planned behaviors considering the conditions of environments (in other words situations). The tasks and behaviors are hierarchically composed and include start conditions for beginning those and termination conditions for stopping those. CGFs first check whether the start condition of the planned behavior for accomplishing a task is satisfied or not in some degree and perform the behavior if satisfied continuously until the termination condition of the behavior will be met. If the termination condition is satisfied, then they check the start condition of the next planned behavior. This process will be repeated for accomplishing the mission. If the situations of CGFs are different by changing the environments from those of planning time, it may cause the start condition of the planned behavior to be dissatisfied. In this case, CGFs can decide a new behavior using fuzzy rule base. We realized our planning system and tested CGFs with a scenario. Experimental results showed that our system worked well and actively coped with situation changes. It will be possible to make CGFs that can do more autonomous behaviors if we continually develop our method.