New neutron reference fields, based on a 239Pu–Be source, intended for increasing the accuracy of measurements of neutron dosimeters and radiometers in the IHEP accelerator complex are described. A Bonner SB-RSU-01 spectrometer was used to measure the spectra of the neutron reference fields. The BON95 code was used to reconstruct the spectra; the initial spectra for the iteration procedure were determined by parameterization or by a calculation using the FAN15 code. Good agreement was obtained between the neutron spectra and the integral characteristics of the reference fields reconstructed by the two methods.