A subdividing method for grating signal based on FPGA was proposed. The method uses CORDIC algorithms and singleprecision floatingpoint calculation, which can implement the function of directionjudgement,counting, phase decoding by CORDIC algorithm, floatingpoint calculation between the two codes on a single FPGA. It can assure the subdivision accuracy, guarantee the effective calculation accuracy of subdivision data, and ensure the computational speed. The simulation was based on chip CycloneIIEP2C20F484C8 of Altera company, by subdividing the signal of grating with 2 μm length period. The result proves the feasibility and validity of this method.