Nearly 200 sets of three-axis fluxgate magnetometers are used in Chinese geomagnetic observatories, but due to their directional errors, it is necessary to study error correction methods to improve measurement accuracy. Experimental results show that correcting the Z-axis and D-axis directional errors is essential. The observation data after error correction demonstrate the clear correction effect. The measurement device used in the experiment is low in cost and easy to disseminate.