Using the data of the ATNF pulsar catalog we study the relation connected the real age t of young neutron stars ( NS ) and their spin-down age \tau .
We suppose that this relation is independent from both initial period of the NS and its initial surface magnetic field , and that the laws of the surface magnetic field decay are similar for all NSs in the Milky Way .
We further assume that the birth-rate of pulsars was constant during at least last 200 million years .
With these assumptions we were able to restore the history of the magnetic field decay for the galactic NSs .
We reconstruct the universal function f ( t ) = B ( t ) / B _ { 0 } , where B _ { 0 } is the initial magnetic field and B ( t ) is the magnetic field of NS at the age t .
The function f ( t ) can be fitted by a power law with power index \alpha = -1.17 .