The harm impact evaluation was studied for pollution accident happened in urban crude water system characterized of fetching crude water from reservoir through channel.The relevant direct and indirect factors to harm impact of crude water pollution accident were analyzed.Furthermore, the attribute reduction method in rough set theory was applied to eliminate the redundancy of indirect factors.Integrating the direct and indirect factors effects, an emergent evaluation model for the HarmImpact was established with the similarity analysis by vague sets theory.Taking crude water system in Chengdu as a case study, a designed nitrobenzene pollution accident was simulated in different workingconditions.Moreover, the Harm Impact extent of the accident was calculated with the proposed model.The sensitivity analysis indicates that the proposed model is reasonable and valid in the emergent evaluation for the pollution accident happened in the urban crude water system.