Abstract: According to geomagnetic daily variation records of national geomagnetic observatory network of China, we analyze the observation data inconsistency by multiple sets of tri-axial fluxgate sensors in the same observation environment. Through theoretical calculations and experimental tests on the geomagnetic station, we got the quantitative relationships between instrument horizontal, orientation and each geomagnetic component. The experiment results show: if there is orientation error angle α, the D component observing curve contains a certain proportion of the H component; in the horizontal plane, if the angle φ is fromed by magnetic sensor rotating around the H component as axis in the ZOD plane, the D component observing curve contains a certain proportion of the Z component; if the angle θ is formed by magnetic sensor rotating around the D component as axis in the ZOH plane, the H and Z component observation curves contain a certain proportion of each other component.