The purpose of the present study is to obtain reduced kinetic mechanisms specifically for the detonation simulation in lean, stoichiometric and rich H2-N2O-Ar mixtures. A recently developed detailed mechanism and a constant- pressure reactor model are chosen to perform the reduction. A method of automatic reduction is used to eliminate redundant chemical reactions while respecting error limitations for several practically important characteristics of the combustion process. Further reduction is made by globalizing a part of the reduced mechanism. Reduced mechanisms are finally validated in ZND detonations simulations.