The invention discloses a method for determining water accumulation depth based on double drainage systems of SWMM. According to the method, the SWMM is utilized to establish a model of a catchment region; extra connection nodes are added along road edges or roadsides; surface side ditches are added into the model; for parallel pipe pairs, underground pipes are located under the surface side ditches by adjusting the bottom elevation in each node and adjusting inlet and outlet skew of the surface side ditches; Full-Street sections and Half-Street sections of the surface side ditches are created; the created Full-Street sections and Half-Street sections are given to the corresponding surface side ditches; and simulation is performed to perform water accumulation depth analysis. Through the method, according to the double-drainage-system theory in the SWMM, street surfaces and side ditches and the like are used as a surface drainage system, a municipal pipe network is used as an underground drainage system, the double-drainage-system model is established, simulation is performed, water accumulation can be analyzed, and collaborative operation of road surface pipes is simulated.