Abstract: The deficiencies of reverse distance weighting method and reverse latitude difference weighting method traditionally used in the calculation of diurnal variation of geomagnetic data are analyzed. According to the characteristics that the geomagnetic field has affinity with the changing of latitude, and considering the influence of latitude and longitude in the calculation of diurnal variation of geomagnetic data, the bifactor weight determination method is proposed. The validity of the proposed method is testified using geomagnetic observatory data supplied by Intermagnet website. Compared with the reverse distance weighting method and reverse latitude difference weighting method, the new bifactor weight determination method has more superiority.Experimental result shows that the proposed method is applicable in the calculation of diurnal variation of geomagnetic data, and it may have wide application prospect in diurnal variation correction of satellite, airborne and seaborne geomagnetic measurement data.