An elaborate analytical model representation of the magnetospheric magnetic field has been developed based on the merged IMP-HEOS experimental data set. As distinct from the approach of Mead and Fairfield (1975), our model incorporates separate mathematical description of the ring current, the magnetotail current sheet and the magnetopause contributions to the total magnetic field. Model formulae for the magnetic field components contain in total 28 input parameters (21 linear coefficients and 7 non-linear parameters) obtained by means of an iterative minimization procedure, which fits the model to the experimental data sets corresponding to different levels of geomagnetic activity, as well as to different conditions in the solar wind.