Abstract: The gird effect fence in DFT spectrum is deeply analyzed. The correction algorithm of amplitude ratio is deduced and the interpolating correction equations with different windowed-functions are derived on the basis of classic Rife algorithm to improve the measuring-frequency accuracy. A method for engineering implementation based on field programmable gate array (FPGA) is also discussed. A novel estimate algorithm of frequency offset for FPGA is provided based on interval search to avoid complex division operation. The simulation result shows that estimate algorithm of frequency offset based on interval search meets well the engineering requirements.