Abstract: Ground and space-based observations of the geomagnetic field are usually a superposition of different sources from the Earth’s core, lithosphere, ocean, ionosphere, and magnetosphere, and also from field-aligned currents coupling the ionosphere and magnetosphere—the meridional currents that connect the two hemispheres and the induced currents due to the variations of fields over time. The fluctuation of magnetic fields generated by these highly dynamic space currents greatly limits the accuracy of the geomagnetic models. In order to better accomplish the scientific objectives of Macau Science Satellite-1 (MSS-1), and to improve existing geomagnetic field models, we present here for the first time a self-consistent coupling of solar wind, magnetosphere, and ionosphere, which represents the most developed numerical simulation method for space physics research so far, making it possible to quantify the contribution of different current systems to the total observed magnetic field (B). The results show that numerical simulation can capture main magnetic disturbance characteristics with significant precision. Partial ring current is a major contributor to the latitudinal magnetic perturbation near the equator. Magnetopause and magnetotail currents affect the radial magnetic perturbation around the mid-latitudes. Field-aligned and Pedersen currents produce significant longitudinal and latitudinal magnetic perturbations at high latitudes.