The modified electrodes of Mo-S-Ag cluster compound films on silver surface were investigated by FT-IR, FT-Raman and XPS. The new modified electrodes were applied to the catalytic oxidation of ascorbic acid. This sort of catalytic effects can be inferred because the oxidation peak potentials of ascorbic acid moved to more negation compared with the bare Ag electrode and the oxidation peak currents increased with the increasing of ascorbic acid concentration. The overpotentials of ascorbic acid were significantly reduced. CV measurement revealed the linear relationship between the oxidation peak current and the concentration of ascorbic acid ranging among 0.001 - 0.06 mol/L.