An innovative framework of mutual adaptive CAI system is proposed in this paper for teaching plant diagnosis knowledge by more human friendly than by conventional CAI method. In order to realize such CAI, a new head-mounted-display, i.e., Eye-Sensing Head-Mounted-Display (ES-HMD), has been developed which will not only provide the user with virtual environment through visual and auditory stimuli but will also monitor the user¡Çs both eyes and calculate ocular information such as pupil size, eyeblink or eye gaze. The obtained ocular information will be utilized for on-line analysis of user¡Çs mental workload, cognitive state and longtime fatigue, because user¡Çs ocular information will reflect on such psychological factors unconsciously while watching display image. Some experimental results are also presented to test eye tracking capability by using the developed ES-HMD.