Abstract: The digital geomagnetic data recorded by GM3 Gaussmeters and FHD-1 Nuclear precession Magnetometers in 2002 and 2003 are compared with the analogue data.The baseline value and its accuracy as well as the correlation between maximum and minimum are analyzed.Through studying the difference of analogue and digital data and its cause, we find out the main factors that affect the quality of the data.It is concluded that digital observation can replace analogue observation.