Researchers have always met with problems like lack of geomagnetic data when processing magnetic data,so it is necessary to estimate geomagnetic data in appointed area.Based on an analysis of diurnal geomagnetic correction with multi-observatories,the authors have found that geomagnetic data of different observatories are linear,so the formula of estimating geomagnetic data can be fitted by importing regression,and then the effects of the method can be checked by using observed data.The reliability of the method is confirmed,which is a progress in data processing.