The assessment of water use benefits is complex as it involves economic, ecological and social domains. The index system of the benefits assessment is multi-object and semi-structural including both quantitative and qualitative indices. Based on the theory of variable fuzzy, the benefits assessment system in an irrigation district in Shanxi province, northwestern China is built. Using the two-level variable fuzzy decision-making model and the improved multi-level decision-making model, the benefits of water use in the irrigation district are assessed in three level years of 1997, 2005 and 2015. The results show that the benefits are gradually increasing, and the multi-level variable fuzzy decision-making model is superior to two-level model which makes the calculation results more stable. Moreover, the multilevel model can not only be used to optimize the different schemes but also to assess the grade of each scheme, with which to support the decision-making for the sustainable development of water use in the irrigation district.