At present, the existing water breakthrough time models in edge-water gas reservoirs are mainly based on the vertical well scheme and ignore the impact of the formation dip angle and non-Darcy flow effect, thus resulting in some differences between the predicted and actual measured data. To improve the accuracy of prediction, we have considered the effect of gravity caused by the dip angle in the edge-water gas reservoir. The established mathematical model of a low permeability edge-water gas reservoir is based on the theory of gas-water two-phase seepage. The prediction model of water breakthrough time in a horizontal well considers the influence of the formation dip angle, starting pressure gradient, and non-Darcy flow effect. The prediction model sensitivity analysis has been carried out. The results show that the predicted time of the new model is closer to the actual water breakthrough time in the gas reservoir than that of the existing models. The sensitivity analysis results show that the water breakthrough time decreases with increase in the gas well production, and increases with increase in formation dip angle, horizontal well length, and original distance between the gas-water interface and the well bottom. For the same horizontal well length, the water breakthrough time calculated considering the non-Darcy flow effect is shorter than the time calculated without considering the non-Darcy flow effect. The research results provide the necessary background for accurate prediction of the water breakthrough time in edge-water gas reservoirs.