With the development of natural gas resources in the sea, the blowout problem in high-production gas wells is becoming increasingly prominent. When the high-production gas well blows out, a large amount of gas carries the drilling fluid outside the well, and the wellbore becomes empty quickly, and the conventional killing method cannot be used. In most blowout cases, the drilling tool is far from the bottom of the hole, and the falling process of kill fluid in the gas below the bit is complicated. Aiming to address the problem of the falling flux of kill fluid in high-production gas wells, this paper studies the falling flux of kill fluid by combining experimental and numerical simulation data. It breaks the single falling criterion of kill fluid. It uses a combination of dimensionless numbers to fit the data, establishing a model for the falling flux of kill fluid. Taking a deep-water accident well as an example, based on the established falling flux model of kill fluid in this paper, the influence of different parameters on the well killing law is analyzed. The results show that the kill fluid’s displacement, density, viscosity, the injection point’s depth, and the drill string’s cross-sectional area are directly proportional to the bottom hole pressure and inversely proportional to the gas production at the bottom of the well. The falling flux of kill fluid determines the time and cost of well killing. Accurately calculating the falling flux is helpful for the success of well killing and provides theoretical guidance for on-site well killing operations.