The combined gravity-magnetic inversion is an effective means to improve the resolution of underground medium imaging and reduce the multi-solution problem of inversion. This paper systematically studies the three-dimensional gravity-magnetic combined inversion method based on the cross-gradient structure coupling. By introducing the cross-gradient operator to construct structural consistency constraints, the collaborative optimization of gravity and magnetic data in the inversion process is achieved. The theoretical model experiments show that this method can effectively enhance the focusing and structural consistency of the inversion results, especially in models with complex anomaly body shapes and significant differences in physical properties. Compared with the single property inversion method, the cross-gradient method significantly improves the spatial positioning ability of the anomaly body while maintaining the rationality of the property values.