Water ecological carrying capacity refers to the degree that natural aquatic ecosystems can support human activities under certain conservation goals, while maintaining ecosystem quality. To explore this concept, which is based on water resources, environmental conditions, and socioeconomic factors, 16 indicators were selected to analyze the multivariate coupling effect of water ecological carrying capacity and to quantify correlations between this effect and related driving factors. A particle swarm optimization gravitational search algorithm-projection pursuit (PSOGSA-PP) model with a function of multiple drivers was established to evaluate water ecological carrying capacity. The Beijing-Tianjin-Ji (Hebei Province) region was chosen as a case study for analyzing the drivers of ecological benefits of regional water resources and water quality and for maximizing the associated economic and social benefits, as well as to evaluate water carrying capacity and impact factors. Scenarios were developed based on carrying capacities during different periods, and water ecological carrying capacity evaluation levels were established using PSOGSAs and the optimal projection direction a, the classification standard threshold projection z'(i), and the projection value of evaluation instance z'(i). Water carrying capacity exhibited an improving trend, from level IV (overload) and level V (extensive-overload) to level Ⅱ (ideal), for 13 cities in the Beijing-Tianjin-Hebei region from 2008 to 2030; projections indicated, for instance, that Zhangjiakou City would remain at level Ⅱ for the most of the period, and attain level I (ideal) by 2030. Our results offer support for the exploitation and utilization of water resources, as well as the protection of aquatic eco-systems, in the Beijing-Tianjin-Hebei region in the future.