Abstract: Based on the Archimedean Principle, building basement floating accident occurs when the groundwater head pressure beyond the foundation pressure. In order to insure the safe of the building, the safe groundwater level height, referred as water level for prevention of up-floating in general, must be confirmed before the design stage. The current different viewpoints on the determination of water level for prevention of up-floating are verified by the examples,and suggestion which may be a reference to the determination of water level for prevention of up-floating is put forward.