At present, there is no particularly effective method to predict the degree of production at the end of the stable production period of gas reservoirs with active edge water. The production often declines rapidly without warning. Based on the physical model of long core of gas reservoirs by water flooding in Yakela area, the characteristics of gas-water two-phase seepage during water invasion are simulated by the experiment of gas recovery by water flooding. Taking the material balance equation of water flooding as the theoretical method, the concept of water invasion coefficient is introduced to describe the water invasion characteristics of gas reservoirs. As the hydrocarbon pore volume（HPV） of the injected water is consistent with the concept of water invasion coefficient, it is feasible to simulate the effect of water invasion on gas reservoir by water flooding experiments. The experimental results show that when the injected water reached 0.3 ~ 0.45 times of HPV, the waterflood front breaks through, and the gas production enters the rapid decline period from the stable production period. The production history shows that when the water invasion coefficients of the middle-lower gas reservoir reach 0.33 ~ 0.36, the gas production decreases rapidly, and the experiment is basically consistent with the production practice. By calculating the water invasion coefficient of upper gas reservoir, when the water invasion coefficients reach 0.33 ~ 0.36 from August 2019 to February 2020, the end of stable production period will come. It is basically consistent with the results of numerical simulation and necessary to adjust the high risk wells in time.