Abstract: In order to study the dynamics of the water resources system and to solve the problems existing in traditional TOPSIS evaluation of water resources carrying capacity, for example, when the evaluation values are close to the interval classification boundary,the grade differentiation is not high, thus it is difficult to form an objective and effective evaluation. In this paper, due to the advantage that D-S evidence theory can effectively reduce loss caused by data variability and fuse the results objectively and accurately, it is used to improve TOPSIS method for water resources carrying capacity evaluation. By fusing the distance between the indicator vectors in TOPSIS method and the positive and negative ideal solutions, the synthetic confidence of each grade of water resources carrying capacity is obtained, and the grade of water resources carrying capacity is judged based on the synthetic confidence value with greater differentiation. On this basis, the indicator increment is introduced to calculate the changes in the water resources carrying capacity over the years, and the time power vector is used to combine the changes over the years to analyze the trend of water resources carrying capacity. The results show that: the discriminations between the evaluation value and the interval boundary are improved from 0.000 3, 0.001 1 in 2018 and 2020 to 0.019 and 0.336 7 respectively by improved the TOPSIS. Meanwhile, the error between the predicted trend using the proposed trend analysis method and the actual result is 0.001 9 in 2020. Finally, it is predicted that the water resources carrying capacity will have a negative trend in 2021. The main impact indicators are annual precipitation and per capita water resources by the obstacle factor model. The suggestions are put forward to strengthen the construction of the ecological environment and optimize the rational allocation of water resources. The method in this paper has higher grade distinction, and the evaluation results are reasonable and objective, in line with the actual situation. And it can also make comprehensive use of the dynamic data of the past years so that it can accurately describe the changes in water resources carrying capacity, which can provide a scientific basis for the development and protection of water resources.