Abstract: Geomagnetic secular variation and short-term disturbance need to be reliably separated from the geomagnetic diurnal observation.In this wise,it will provide a definite datum for correction to geomagnetic data,and guarantee accuracy of data fusion for different cruises.In the case of good coverage of the geomagnetic diurnal observatory for marine geomagnetic survey,for the secular variation at the survey area to be corrected by that at the geomagnetic diurnal observatory,the geomagnetic normal field fixed at anuni form time would be adopted to become a datum for geomagnetic anomalies at both the geomagnetic diurnal observatory and the survey area.Otherwise,for the secular variation at the survey area to be corrected by the geomagnetic normal field,the geom agnetic normal field changing with time would be adopted to become a datum for geomagnetic anomaly at both the geomagnetic diurnal observatory and the surveyarea.Thus,the base value for geo magnetic diurnal variation correction maybe explicitly defined to be a sum of the geomagnetic normal field and geomagnetic anomaly.Geomagnetic anomaly at the diurnal observatory can be obtained to average the deviation of the geomagnetic total field obser vation from the geomag netic normal field at some way.Geomagnetic disturbance may be at tentively separated to maintain continuous transition to the disturbance beginning and end.The comprehensive model can be adopted to unitedly perform corrections for diurnal variation,normal field and its secular variation,which will preferably solve problems arisen in diurnal variation correction.