According to hydraulics, a new formula has been deduced from a thin free steady orifice outflow. It can be used to evaluate the water storage in bearing-media in the tunnel project by using the discharge of the bore-hole or fracture. The formula can also be used to predict or calculate the discharge in the future or in the early days. There are no any parameters about the bearing-media and the shape of the bore-hole or fracture involved in the formula. Therefore, it is simple and easy to 6e conducted.