The accuracy of geomagnetic vector observation data will be affected by Instrument orientation error, and the existing correction methods require known geomagnetic field modulus or referring to standard instruments, and are difficult to be applied in downhole and marine situations where manual installation and adjustment of instruments are impossible. A large dynamic fluxgate magnetometer and a vector correction method based on Euler rotation transformation are proposed by the paper. The directional error angle of fluxgate can be obtained and the measurement is self-calibrated by this method without referring to standard instrument. The results show that when the orientation error of experimental instrument is set to the large angle of four different quadrants, the correlation coefficient with the corresponding component of station is still above 0. 99 after correction, and the length of confidence interval in the Bland-Altman diagram is reduced by more than 86% and the RMS error is reduced to less than 15% , which proves the effectiveness of this method. Correspondingly, the observation data quality of geomagnetic stations can be improved, and reference solutions for the orientation of downhole and marine geomagnetic observations can be also provided.