Taking Weihe River as the research object, based on the hydrological survey data of six main sections which are Beidao,Linjiacun,Weijiabao, Xianyang, Lintong and Huaxian of the Weihe River mainstream from 1971 to 2014, we classified the ecological types and calculated the optimal environmental flows (e-flows) of the sections according to their respective environmental characteristics. On this basis, the spatio-temporal differentiation characteristics and guarantee rate of e-flow in Weihe River are revealed. According to the results, the minimum runoff values of the sections are recommened as their e-flows which are 5.68 m3/s, 2.51 m3/s, 11.39 m3/s, 25.33 m3/s, 77.26 m3/s and 61.86 m3/s respectively for Beidao, Linjiacun, Weijiabao, Xianyang, Lintong and Huaxian sections during dry season. The maximum value of e-flow of each section occurs in the flood season (from July to September), and the minimum value in the dry season (from December to March). Except for the flood season, monthly average of e-flow in each section is consistent as a whole. The e-flows of the six sections have no significant difference (P>0.05) between August and January, February, March, April, June, October, November and December, but there is a significant difference between any other two months (P<0.05). Spatially, the e-flow of Linjiacun section in January is the smallest and Huaxian section in August is the largest, which reflects the environmental characteristics of insufficient e-flow in the upstream and sediment deposition in the downstream of Weihe River. The e-flow is generally low in the upstream and high in the downstream. There is no significant difference in monthly e-flow (P>0.05) in Weijiabao and Huaxian; however the differences among the other sections are significant (P<0.05).