Wuhu-Shanghai Canal is an important inter-provincial trunk channel, and it was planned to renovate and meet Grade III standard navigable waterway. The Gucheng Lake is an important source of drinking water, and the Wuhu -Shanghai canal navigation will reduce the quantity of the Gucheng Lake substantially. In this study, the variation of water quantity in the Gucheng Lake after the renovation were calculated by modeling. The results show that opening-gate 10 times per day will result in the water losses of 1.71×108 m3 /a, and the loss is 2.87×108 m3 /a for 20 times per day. The normal water level of the Gucheng Lake is 9.5m, corresponding to storage capacity of 1.28×108 m3 . The Gucheng Lake will loss normal water quantity by 133.6% and 224% if the renovation is completed and open to navigation. In addition, if the gate open 20 times per day, the Gucheng Lake will have to supplement water quantity to meet the water demand. If the preparation reach 90% of that in normal year, the Gucheng Lake need 0.64×108 m3 supplement water per year，which is almost half of the storage capacity of the Gucheng Lake.