Field source boundary identification is an essential task for interpreting field data, and normalized magnetic source strength (NSS) has become the main method for interpreting magnetic data because it is not affected by magnetization direction. This paper addresses issues related to near-field boundary identification, the divergent effects of single and multiple magnetic source boundary recognition, and the challenges of identifying the geometric boundaries of magnetic sources that are far apart and experiencing mutual coupling during multiple magnetic source boundary identification. A new magnetic target boundary identification method has been proposed, which uses second-order partial derivatives in the inclined angle boundary identification method and introduces NSS. This method is applied to the boundary identification of a single rectangular magnetic source, three rectangular magnetic sources in the same plane, as well as boundaries of deep and shallow anomalies. The simulation results indicate that the method proposed in this paper not only leverages the advantage of NSS in reducing the coupling effects between magnetic sources and the insensitivity of depth to inclination angle, but also allows the recognized magnetic source boundaries to converge more effectively by using second-order partial derivatives.