Praseodymium hexacyanoferrate film was modified on the graphite electrode by cyclic voltammetry in the solution of PrCl_3 and K_3Fe(CN)_6. Its electrochemical properties, including the influence of different scan rates, ions, and K~+ concentrations on the film, were studied. The membrane was characterized by IR and XPS. In IR spectrum, the vibration of cyano group verified from the formation of the film on the electrode. In XPS spectrum, the splitting of Fe2p_(1/2) )and Fe2p_(3/2)) showed that the valence of iron has been changed in the film formation, and a proper electropolymerization mechanism was put forward. The results showed the PrHCF film have some electrocatalytic activity to the oxidation of cysteine. The detection conditions for cysteine such as the potential and pH were also discussed.