Based on Hu's histogram Monte Carlo method and the Swendsen-Wang algorithm, we calculate the geometrical factor of the q-state bond-correlated percolation model corresponding to the q-state Potts model (QPM). The free energy f, the internal energy U, and the specific heat Ch of the Ising model, i.e., the QPM with q = 2, calculated from this geometrical factor agree very well with exact results. This histogram-importance sampling Monte Carlo method is very simple and has many potential applications.
