  Electric and magnetic screenings of the thermal gluons are studied by using
the background expansion method in a gluodynamic model with dimension-2 gluon
condensate. At low temperature, the electric and magnetic gluons are
degenerate. With the increasing of temperature, it is found that the electric
and magnetic gluons start to split at certain temperature $T_0$. The electric
screening mass changes rapidly with temperature when $T>T_0$, and the Polyakov
loop expectation value rises sharply around $T_0$ from zero in the vacuum to a
value around 0.8 at high temperature. This suggests that the color electric
deconfinement phase transition is driven by electric gluons. It is also
observed that the magnetic screening mass keeps almost the same as its vacuum
value, which manifests that the magnetic gluons remains confined. Both the
screening masses and the Polyakov loop results are qualitatively in agreement
with the Lattice calculations.
