The invention discloses a method for obtaining a resonance group constant by aiming at the dual heterogeneous fuel of a nuclear reactor. On the basis of an ultrafine group resonance calculation method, an energy spectrum obtained by solving a neutron slowing-down equation by a lattice cell of which the fuel region is homogenized and a point section corrected by a Shmakov method on the basis of a dual heterogeneous geometrical parameter are subjected to merging on the basis of volume flux weight to obtain the resonance group constant. Compared with a non-deterministic theory Monte Carlo method, the method disclosed by the invention can obviously improve calculation efficiency and economic efficiency. Meanwhile, the coupling of two methods enables a deterministic theory ultrafine group resonance calculation method to own a capability of processing a complex dual heterogeneous geometric resonance problem, the application of the ultrafine group resonance calculation method can accurately process a resonance interference effect which is in the presence in fuel and can obtain accurate homogenized resonance group constant.