Estimation models of economic losses due to flood are established by combining drainage times of urban road waterlogging-theoretical models and economic loss assessment models, etc. And then the "loss" curves are determined by discussing the relationships between daily mean precipitation and economic losses of urban transportation departments. Some socioeconomic variables, which are closely related to the anti-flood capability of urban transportation departments, are adopted in the models in this paper. By model testing, the economic loss assessment model established in this paper shows good simulation performance and applicability. And it has simple computation, needs few input variables, and is suited for the rapid assessment of the economic loss of some region. Based on the models established in this paper, the thresholds of the precipitation intensity and the total storm precipitation of each year in Shanghai are calculated. And a new definition of extreme precipitation, called "fixed thresholds varying with the influence factors", is given. This definition underlines the socioeconomic character of extreme precipitation which would cause economic loss and possesses high social practical values compared with other definitions of extreme precipitation.