  We report the detection of a 282 $^{+34}_{-31}$ pc-sized core in the center
of Milky Way dark matter halo at $68\%$ confidence level by using the
micro-lensing event rate sky map data from the Optical Gravitational Lensing
Experiment (OGLE) survey. We apply the spacial information of the micro-lensing
sky map and model it with the detailed Milky Way dark matter halo Core/Cusp
profile, and the fraction of dark matter in the form of Mini Dark Matter
Structure (MDMS, $f_{\rm MDMS}=\Omega_{\rm MDMS}/\Omega_{\rm DM}$), e.g.
primordial black hole, earth-mass subhalos, floating planets and so on. We find
that this sky map can constrain both $f_{\rm MDMS}$ and the core size
simultaneously without strong degeneracy while fully considering mass function
of Milky Way stellar components from both the bulge and disk.
