In order to measure the problems of randomness and fuzziness during the river water security assessment, a cloud model is introduced, and the importance of determining vector standardization was discussed. Based on the measured values and the evaluation threshold, the index’s quantitative certainty vector to the collection of comments is generated. And then the comprehensive certainty vector of river water security is calculated based on the weight, and the level of river security is determined. Taking Zhong Canal which is the major channel in the eastern route of SouthtoNorth Water Diversion Project as an example, the author of paper made a water security assessment. The results show that the river security level of Zhong Canal is “good” in the year of 2012; compared with the assessment results by fuzzy synthetic model and set pair analysis model, the cloud model is an effective model of river water security assessment.