Abstract: The acquired data accuracy has been a key factor in the underground geomagnetic positioning.To study the geomagnetic data fluctuations during the time domain in underground,the geomagnetic data of the six datum points in three solar days have been monitored by the FVM400 magnetometer in some mine,preprocess and statistical analysis of the different points.The results show that there is a same fluctuation rule between three-component data and geomagnetic total field of single point,which is the measured stability time domain of 00:00—08:00 and 16:00—24:00,and the instability time domains is 08:00—16:00.There is slight differences which range from 20 nT to 60 nT,and reach the maximum fluctuation at 12 o'clock.It is relatively stable to measure the data fluctuation at multiple points during the same time,differences of the geomagnetic data of the adjacent points which eliminate most of the impact of the time domain fluctuation in the underground geomagnetic positioning.