The change of Dianshan Lake during the Song and Yuan dynasties are the result of the changes of hydrological environment in the east of the Taihu Lake. During the mid to late Northern Song Dynasty, Dianshan Lake was expanded due to crustal subsidence in the Dianmao (淀泖)region, the siltation of the Wusong River, and the accumulation of water in the pond, and the main flow of Dianshan Lake was discharged into the Wusong River along the northern ponds, forming a unique overflow hydraulic system between the Wusong River, the ponds along the river and Dianshan Lake. During the Southern Song Dynasty, the drainage pattern of Taihu Lake was southeast and northeast, influenced by the continuous siltation of the Wusong River, and the clear water and tidal water were permanently supported by each other in the northeastern waters of Dianshan Lake, resulting in the spread of siltation and the expansion of polder. The backwater of Dianshan Lake, which has been blocked from flowing northward, gradually develops towards the southeast. During the Yuan Dynasty, the main stem of the Wusong River continued to silt up, the amount of water coming into Dianshan Lake continued to increase. However, with the blockage of the outlet of Dianmao in the northeast pond and the construction of the southeast pond, the water was stagnant in the Mao area, including Dianshan Lake, causing a stagnant catchment area and a second expansion of Dianshan Lake.