In March 2012, the Cabinet Office, government of Japan published a new model of the Huge NANKAI Trough Earthquake, and it is assumed that the seismic motion will be bigger and tsunami will be higher than traditional model. Therefore, the need of disaster preparedness to avoid such mega‒risk is becoming more important than ever in Japan. Since the Great East Japan Earthquake, Japan's economic activities and people's lives have been distressed due to the shortage of mid and long term power supply. From this aspect, it is needless to mention that the shortage of power supply is one of the critical issue for achieving recovery and reconstruction after the disaster. Hence, in order to avoid repeating the same power supply problem in the future when the Huge NANKAI Trough Earthquake hit Japan, estimating post‒disaster power supply and demand throughout the mid and long term beforehand is crucially important. Thus, in this draft, a new method of estimating post‒disaster power supply and demand gap throughout nine months is shown.