  We study 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 decays lead to the flattening of central density
and overall reduction of 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 observation of local
dwarf galaxies. Our results suggest that the DDM holds great potential for
resolving the small-scale problems faced by the cold dark matter (CDM) model.
