Mann-Kendall trend test and change points test were used to analyze the change trend and abrupt point of water resources in recent 50 years for urbanized Suzhou City. The double mass curve and climate elasticity model are chosen to assess the impact degree of main driving factors on water resources changes quantitavively. The results show that the series had significant increasing trends; and mutation features occurred in 1991. The climate change and human activities are the main driving factors for runoff change; both led to the increase of runoff. Quantitative assessment results of double mass curve the climate elasticity model are similar; the contribution rations of climate change on runoff change both exceeded 50%,and were 62% and 77% respectively. The impact proportions of human activities on runoff change are 38% and 23% respectively. The conclusions can provide the decision-making basis for the planning and design of the sponge city in Suzhou City.