Cross-regional water diversion projects usually face risks of hazards, in particular high risks of sudden landslides on the slopes of water supply open channels. Determining the hazard level rapidly after a hazard occurs plays a critical role in improving the efficiency of emergency response and recovering the water supply capacity of the projects. Through in-depth analysis of the factors that affect the severity of open-channel landslides, an indicator system for hazard assessment of open-channel landslides was established and the criteria for evaluation of different hazard levels were identified. Based on the hierarchy of the indicator system, a two-level fuzzy comprehensive evaluation model was established to assess the impact of indicators in the model on the hazard level of open-channel landslides, and the weight of each indicator was determined by the analysis hierarchy process. The linear function was used to calculate the membership degree of each indicator to determine the hazard level. A hazard scenario was created with the water diversion project from the Irtysh River to Urumqi as an example, and the two-level fuzzy comprehensive evaluation model was applied to conduct hazard assessment. The proposed method was confirmed to be reasonable and practical.