Waterseepage is one of the common and dangerous incidents in the construction of deep foundation pits. In the paper, the causes for the waterseepages are studied in terms of hydrogeology, construction methods and water level monitoring. The effect of water level monitoring in the construction of deep foundation pits is emphatically discussed. Improved methods and timing of water level monitoring are proposed. The practice demonstrates that water seepage incidents can be avoided or can be timely coped with by comprehensive analysis on the water seepage risks.