A numerical model is worked out for the magnetosphere, which provides a description of the geomagnetic field out to distances similar 50 R//E. The model incorporates the following field sources: a geomagnetic dipole, the current layer of the tail, which has a finite thickness, the ring current and system of currents on the magnetopause. The latter is found from the condition for a zero resultant field outside the magnetosphere. The parameters of the field sources, as well as the shape of the magnetosphere, are stipulated in accordance with experimental data. The results of calculations of the configuration of the lines of force and the deviation of the resultant geomagnetic field for a dipole field are in good agreement with the measurements.