Using active site model molecules consisting of similar to 100 atoms, the reduction potentials of five type-1 Cu centers in cucumber stellacyanin, fern dryopteris crassirhizoma plastocyanin, Met148Gln rusticyanin, wild type rusticyanin, and Met148Leu rusticyanin were calculated with a heterogeneous conductor-like polarizable continuum model and the B3LYP/6-311++G(2df,p) method. The results are 242, 366, 522, 667, and 825 mV, respectively, in good agreement with experimental values 260, 376, 563, 667, and 798 mV. Ligand interaction (similar to 250 mV) and solvation effect (similar to 250 mV) are found to be the main determinants of the relative E-0 of these five type-1 Cu centers.