Kalman filter is widely applied in engineering due to its real time recursive algorithm, while it is hard to implement hardware with traditional device in some actual systems with hign performances in real time and in flexible and convenient implementation. Applying plentiful resources of FPGA and its flexibility and parallel computation, according to the "first timing later circuit" mind, this paper designed a floating Kalman filter by using the top-down synchronous design method based on FPGA. The design uses time-sharing multiplex technology in IP cores and modules so as to save resources and to implement hardware conveniently on the premise that the system has met the real-time requirement. Taking the precision improvement of the GPS as its application, the Modelsim simulation results show that the designed floating Kalman filter is real time and easy to realize and simultaneously saves hardware resources, so it has practical value.