Abstract: The secondary gamma and neutron spectra induced mainly by the galaxy cosmic rays (GCR) may represent the elementary composition and the water ice content of the lunar regolith, which has a special significance to the next phase of lunar exploration and in situ utilizations. In this paper, the Monte Carlo method is used to simulate and analyze the secondary gamma and neutron radiation on the lunar surface under the galactic cosmic ray environment. It is shown that the gamma spectrum has obvious hydrogen (2.23 MeV), aluminum (0.83 MeV), calcium (3.53 MeV), oxygen (6.13 MeV), silicon (1.77 MeV) line characteristics, with little effect of the water content, except that the hydrogen line becomes more obvious for higher water content; while the lunar neutron spectrum is closely related to the water ice content in the lunar soil in that the thermal neutron flux decreases with the increase of the water ice content. The flux of 0.01eV neutron for 20% water content decreases by 72% compared with that of the non-aqueous soil. We therefore recommend to use small, low-power neutron & gamma composite detectors in the following lunar plan to realize the in situ lunar gamma neutron radiation environment detection first in China, and to accumulate basic data for the inversion of lunar water resources and mineral resources for future explorations.