Abstract: Currently, predicting the timing of water breakthroughs inedge-water gas reservoirs, only the water mass point tonguing is taken into account while the effect of reservoir dip and water invasion on water migration are ignored. Disregarding the effect of dip and water invasion creates a problem, and the predicted water breakthrough timing does not agree with actual results. In order to predict water breakthrough timing more accurately, the effect of both reservoir dip and water invasion were taken into consideration based on material balance equation and fluid flow theory in porous media. Based on the driving force of mass point flowing and the gravity along the dip direction, the migration of reservoir water was divided into a water invasion stage and a tonguing stage, and then a novel model was developed to predict water breakthrough timing in edge-water gas reservoir with certain dip. The effect of reservoir dip and water invasion on water breakthrough timing were studied in this model. Results demonstrated that the water invasion rate is inversely proportional to the water invasion time, and the reservoir dip is non-linear with the tonguing time primary increases then decreases. The case study showed that the predicted water breakthrough timing of this newly established model is closer to the actual. Results demonstrated that the effect of reservoir dip and water invasion shall be taken into account when water breakthrough timing of edge-water gas reservoirs is predicted. This new model may provide a theoretical basis for analyzing the advancing mechanisms of edge water with dip and predicting water breakthrough timing, as well as an instructive significance in the development and management of gas reservoirs with edge water.