An Office Building is a complex project composed of a tower, podiums and basement. Drainage and decompression design method is adopted in basement anti-floating design. This method guides groundwater to collecting wells by setting gravel hydrophobic layer and drainage blind ditch under the floor of basement, thus, the buoyancy effect of groundwater on the floor can be reduced or even eliminated. The results of finite element analysis show that the seepage of basement is controllable and meets the requirements of regulations. Comparing drainage and decompression design with installation of uplift piles, we find the former method could take advantage in terms of money and time. Theoretically, it is also safer because the basement floor is not subject to buoyancy. It is suggested that the design method of drainage and decompression should be considered in the anti-floating design of basement floor in similar engineering cases.