  The improved quark mass density-dependent model (IQMDD) based on soliton bag
model is studied at finite temperature. Appling the finite temperature field
theory, the effective potential of the IQMDD model and the bag constant $B(T)$
have been calculated at different temperatures. It is shown that there is a
critical temperature $T_{C}\simeq 110 \mathrm{MeV}$. We also calculate the
soliton solutions of the IQMDD model at finite tmperature. It turns out that
when $T<T_{C}$, there is a bag constant $B(T)$ and the soliton solutions are
stable. However, when $T>T_{C}$ the bag constant $B(T)=0$ and there is no
soliton solution, therefore, the confinement of quarks are removed quickly.
