In view of the two-step drainage mode of municipal drainage and water conservancy drainage in urban local flood control, a set of theoretical systems and methods was put forward to reasonably solve the problem of two-step drainage standard matching. By investigation of the nature of the connection between municipal drainage and water conservancy drainage, it was revealed that there are two kinds of risks resulting from design standard matching between municipal drainage and water conservancy drainage: the municipal drainage system cannot timely drain the rainstorm within the design standard of water conservancy drainage into the urban river network; the water conservancy drainage system cannot timely drain the rainstorm within the design standard of municipal drainage into the external receiving water body or retain it in the urban river network. The causation of the two kinds of risks was also revealed: under the condition that rainstorm within the water conservancy drainage duration does not exceed the design value, the rainstorm within the municipal drainage duration exceeds the design value; under the condition that rainstorm within the municipal drainage duration does not exceed the design value, the rainstorm within the water conservancy drainage duration exceeds the design value. Thereby, the risk analysis model for analyzing the two-stage standard matching relationship was established based on the two kinds of matching risks, and finally, a set of methods for solving the model was proposed based on the Copula function. A case study on the standard matching between municipal drainage and water conservancy drainage in Guangzhou downtown was conducted. The results indicated that the first kind of matching risk is relatively high and decreases significantly with the improvement of the municipal drainage standard; the second kind of matching risk is low and decreases with the improvement of the water conservancy drainage standard. At present, the drainage standard of municipal pipe network in Guangzhou downtown is formulated regarding the design rainstorm occurring once every one to three years, and the water conservancy drainage standard is formulated regarding the design rainstorm occurring once every 20 years, therefore, the first kind of matching risk is not less than 15. 63%, while the second kind of matching risk is less than 1%. Comprehensive measures, such as source control, improvement of drainage pipe network, construction of urban waterlogged drainage channel, and optimization of operation management, should be taken to improve the municipal drainage standard. If the municipal drainage can reach the standard of once-in-a-decade or once-in-two-decade rainstorm by adopting comprehensive measures, the average value of the first kind of matching risk can be reduced to 4. 42% or 2. 26%.