Azimuth is a key parameter in well trajectory description， but the conventional measurement with MWD usually exists errors because of the complex geomagnetic field and magnetic field interference. To investigate the impact of bottom hole assembly（BHA） magnetic field interference on azimuth measurement， the interference magnetic field of different drilling tools were measured with a portable magnetometer. On the basis of the interference magnetic field experiment measurement， magnetic pole strength of different drilling tools can be acquired through the data fitting method. With the magnetic pole strength， the interference magnetic field strength can be calculated using the superposition principle， and the azimuth error induced by the interference magnetic field was quantitatively analyzed. According to the experiment results， the interference magnetic field strength along the drilling tool axis exponentially decreases with the added distance and finally goes to zero. Compared to the traditional methods， azimuth error correction using the magnetic pole strengths of drilling tools in this study is more direct and convenient.