  We report a novel search for the cosmic ray boosted dark matter using the
100~tonne$\cdot$day full data set of the PandaX-II detector located at the
China Jinping Underground Laboratory. With the extra energy gained from the
cosmic rays, sub-GeV dark matter particles can produce visible recoil signals
in the detector. The diurnal modulations in rate and energy spectrum are
utilized to further enhance the signal sensitivity. Our result excludes the
dark matter-nucleon elastic scattering cross section between 10$^{-31}$cm$^{2}$
and 10$^{-28}$cm$^{2}$ for a dark matter masses from 0.1 MeV/$c^2$ to 0.1
GeV/$c^2$, with a large parameter space previously unexplored by experimental
collaborations.
