The south bank of Qiantang River, which has been invaded by the tide since ancient times, built a river (sea) pond to keep one side safe. Most of the early dikes were piled up with soil, but the remains of the Xijiangtang and Beihaitang, collectively known as Xiaoshao Seawall, are unknown when they were first built. Xijiangtang north from Xixing Street Yongxing Gate, through the Changhe, Puyan, into Xiaoshan Wenyan town. Beihai Tang west from Xixing Yongxing Gate, and Xijiangtang, east extension into Xiaoshan. Xiaoshao Seawall is a great ancient water conservancy project, which has great significance for the study of ancient river construction technology and Qiantang River geological change.