With the domestic borehole magnetometer, the authors calculated magnetic azimuth in the nonmagnetic interference hole and introduced the concept of Δβ, which is called magnetic azimuth anomaly. The relationship between the symbol of Δβ and the direction of ΔH was clarified, and the relationship between the figure of Δβ and the magnetic body position was obtained. It is thus held that we can use Δβ as an auxiliary parameter in the calculation of magnetic source position.