  Magnetic reconnection plays a crucial role in the energy release process for
different kinds of solar eruptions and activities. The rapid solar eruption
requires a fast reconnection model. Plasmoid instability in the reconnecting
current sheets is one of the most acceptable fast reconnection mechanisms for
explaining the explosive events in the magnetohydrodynamics (MHD) scale, which
is also a potential bridge between the macroscopic MHD reconnection process and
microscale dissipations. Plenty of high resolution observations indicate that
the plasmoid-like structures exist in the high temperature solar corona, but
such evidences are very rare in the lower solar atmosphere with partially
ionized plasmas. Utilizing joint observations from the Goode Solar Telescope
(GST) and the Solar Dynamics Observatory (SDO), we discovered a small-scale
eruptive phenomenon in NOAA AR 13085, characterized by clear reconnection cusp
structures, supported by Nonlinear Force-Free Field (NLFFF) extrapolation
results. The plasmoid-like structures with a size about 150 km were observed to
be ejected downward from the current sheet at a maximum velocity of 24
km$\cdot$s$^{-1}$ in the H$\alpha$ line wing images, followed by enhanced
emissions at around the post flare loop region in multiple wave lengths. Our
2.5D high-resolution MHD simulations further reproduced such a phenomenon and
revealed reconnection fine structures. These results provide comprehensive
evidences for the plasmoid mediated reconnection in partially ionized plasmas,
and suggest an unified reconnection model for solar flares with different
length scales from the lower chromosphere to corona.
