Errors arising due to linearization and spherical approximation of the fundamental equation of physical geodesy can be weaken by replacement of the standard normal field generated by an equipotential ellipsoid. A low-frequency part of one of the modern global models of the geopotential can be used as a new normal field. Here the iterative procedure of refinement of the standard normal field is described and the results of corresponding numerical experiments is shown. We have used here first 70 harmonics of the model GO_CONS_GCF2_DIR_R5 as a new normal field. We are given 6169 points by their geodetic coordinates B, L, h. These points are located all over the USA territory. Two sets of values of height anomaly and the disturbing potential — with reference to the WGS84 normal field and with reference to the new normal field — were calculated. Statistics of the experiment have shown that the values of the disturbing potential and height anomaly decrease more than by 28 times when using the new normal field. Therefore proposed refinement of a normal field can be of use when solving problems dealing with assumptions about smallness of disturbing potential, closeness of artificial telluroid to the real Earth etc. At the same time additional computing expenses are insignificant. The iterative procedure converges in two-three steps and do not take much computational capability and time.