Using a simple model of the neutral sheet current, the relationship between the large-scale distribution of the neutral sheet current and the lobe magnetic field at X=-18 RE is examined. The current is assumed to flow duskward along parabolic curves and return dawnward through the semicircular paths along the high-latitude magnetopause, and the intensity of the neutral sheet current is expressed by using a power law function of the distance from the Earth. A series of tests are performed to find the relative importance of physical parameters in the model. It is found that the lobe magnetic field depends significantly on the radial gradient and the flow-line curvature of the neutral sheet current as well as on the current intensity. We predict that the radial gradient of the current intensity becomes steeper after the expansion onset of substorm. ¿ American Geophysical Union 1994