As the low accuracy, low stability and highly cost of hardware resource of FIR filter using fix-point, a design scheme to realize a FIR filter using floating-point based on FPGA was introduced. It is successful to improve the accuracy of FIR filter and efficient to reduce the error of integer FIR filter`s ratio by using the floating-point arithmetic units. Not only the filter has successful apply to demodulating the Laser Gyroscope signal, but also has powerful portability and great extern application.