Abstract: Amodel of the continuous equatorial-neutral sheet is developed. This model is expressed with a smooth function, whose parameters are determined by the magnetic data of the ISEE-2 satellite, and it can very smoothly connect the geomagnetic equatorial plane with the magnetotail neutral sheet changing about with the earth's tilt angle. Based on this analytic model, a normal curve coordinate system is set up, in which the neutral sheet become one of the coordinate surface. The new coordinate system will change with the earth's tilt angle and thus can almost offset the tilted effect on the pattern of geomagnetic field in the magnetotail region.