Ultra wide band (UWB) technology is widely used in indoor three-dimensional positioning system because of its wide bandwidth advantage and outstanding anti-narrow band interference ability. However, the high cost of base stations limit widespread use of UWB technology. At present, mainstream UWB positioning algorithms need to use four base stations, and the calculation process is complex. This paper proposes a three-base-station UWB location algorithm based on TOF (time of flight). The proposed algorithm also simplify the calculation procedure of 3D positioning, using three base stations, which effectviely reduces the cost of adoption for UWB 3D positioning system.