  In this paper, we study the energy conversion and spectra in a corona current
sheet by 2.5-dimensional MHD numerical simulations. Numerical results show that
many Petschek-like fine structures with slow-mode shocks mediated by plasmoid
instabilities develop during the magnetic reconnection process. The termination
shocks can also be formed above the primary magnetic island and at the head of
secondary islands. These shocks play important roles in generating thermal
energy in a corona current sheet. For a numerical simulation with initial
conditions close to the solar corona environment, the ratio of the generated
thermal energy to the total dissipated magnetic energy is around $1/5$ before
secondary islands appear. After secondary islands appear, the generated thermal
energy starts to increase sharply and this ratio can reach a value about $3/5$.
In an environment with a relatively lower plasma density and plasma $\beta$,
the plasma can be heated to a much higher temperature. After secondary islands
appear, the one dimensional energy spectra along the current sheet do not
behave as a simple power law and the spectrum index increases with the wave
number. The average spectrum index for the magnetic energy spectrum along the
current sheet is about $1.8$. The two dimensional spectra intuitively show that
part of the high energy is cascaded to large $kx$ and $ky$ space after
secondary islands appear. The plasmoid distribution function calculated from
numerical simulations behaves as a power law closer to $f(\psi) \sim \psi^{-1}$
in the intermediate $\psi$ regime. By using $\eta_{eff} = v_{inflow}\cdot L$,
the effective magnetic diffusivity is estimated about
$10^{11}\sim10^{12}$~m$^2$\,s$^{-1}$.
