Abstract: The ground-airborne frequency-domain electromagnetic (GAFDEM) method exhibits high efficiency and low cost compared to conventional ground electromagnetic methods. It is applicable to electromagnetic sounding in complex topographic and geomorphic settings, demonstrating promising application potential. Despite the development and preliminary application of GAFDEM-related instrumentation and equipment, the interpretation methods for GAFDEM data remain under-studied. By investigating the resistivity-varying patterns of three components of the magnetic field in a homogeneous half-space, this study proposed an iterative method based on Taylor series expansion to calculate the global apparent resistivity. Through the calculation of a typical stratigraphic model, this study analyzed the characteristics of global apparent resistivity under different components, frequency domains, flight altitudes, and offsets. The results demonstrate that the definition method of global apparent resistivity in this study, subjected to minimal impacts from parameters like receiver-transmitter distance and flight altitude, can effectively reflect the variations of formation resistivity. Therefore, this study provides a theoretical guide for the processing and interpretation of GAFDEM data.