As aging progresses, fall accident of the person using the walker is an acute problem. It is necessary to know the situation of the user's fall to prevent it. In this paper, we propose a method for estimating the user's fall by modeling of the user in real time as a solid body link model, and pay attention to the center of gravity of the model. We also propose a method for controlling a passive intelligent walker to prevent the user's fall according to the support polygon and the walking characteristic of the user. We experimented with passive intelligent walker in which we implement the proposed fall prevention control and show the effectiveness of the proposal method.