In this paper, the method is applied to analyze and interpret the magnetic anomalies in the Beiya iron-gold mining district, Heqing, Yunnan Province. The emphasis is placed on the calculation of the depths of field sources of each order details and 4th-order approximation on the basis of power spectrum analysis. The results in this study show that the orebodies are responsible for highly magnetic anomalies in the northern and western parts of the Beiya iron-gold mining district, and display the modification in occurrence at the medium-deep parts of it. The results outlined above may inspire some new approaches to the further deep-seated exploration and development in the study area.