  Pure gauge glueballs at finite temperature are investigated in a large
temperature range from $0.3T_c$ to $1.9T_c$ on anisotropic lattices. Optimized
glueball operators are used to obtain better signals. It is found in all 20
symmetry channels that the pole masses $M_G$ of glueballs remain almost
constants when the temperature approaches the critical temperature $T_c$ from
below, and start to reduce gradually with the temperature going above $T_c$.
The glueball correlators in $0^{++}$, $0^{-+}$, and $2^{++}$ channels, are also
analyzed based on the Breit-Wigner ansatz by assuming a thermal width $\Gamma$
to the pole mass $\omega_0$. While $\omega_0$'s are insensitive to $T$ in the
whole temperature range, $\Gamma$'s exhibit distinct behavior below and above
$T_c$: They are only few percents of $\omega_0$ when $T<T_c$, but grow abruptly
when $T>T_c$ and reach values of roughly $\Gamma\sim \omega_0/2$ at $T\approx
1.9T_c$.
