Aiming at solving the problem of water resources carrying capacity evaluation influenced by various uncertainties and ambiguous factors, we proposed a fuzzy variable decision model based on fuzzy set theory, whose parameter weight vectors and the model itself are adjustable and the errors can be effectively reduced. According to the different importance level of different influencing factors, the game theory method was used to integrate the index entropy weight with the worst deviation weight to determine the comprehensive weight of the water resources carrying capacity index. Finally, the variable fuzzy decision model and method were applied to the comprehensive evaluation of water resources carrying capacity in Gansu Province from 2006 to 2015, and the results were verified by the existing findings. The results showed that the water resources carrying capacity of Gansu Province showed a decreasing trend in 2006-2015. It is found that the evaluation results of the grey fuzzy variable decision model are accurate and the differentiation effect is obvious. Our results can also guide the other analyses of local water resources carrying capacity.