Abstract We have studied the density profile of a dwarf halo in the decaying dark matter (DDM) cosmology, using a new algorithm that resolves halo density profiles down to the innermost 700 pc robustly with high efficiency. Following Schwarzschild’s orbit-based method, we have also developed a simplified model to calculate the DDM halo density profiles, which agree remarkably well with those from N -body simulations. Both zoom-in simulations and the simplified model reveal that dark matter decay leads to the flattening of the central density and an overall reduction of the density in dwarf halos, and the underlying physics mechanisms are well illustrated by the simplified model. The slowly rising scaled rotation curves of DDM dwarf halos agree with the observations of local dwarf galaxies. Our results suggest that DDM holds great potential for resolving the small-scale problems faced by the cold dark matter model.