A series of F-doped rare-earth superconductors RBa2Cu3OxFx were synthesized with CuF2 as one of the reactants. According to comparative experiments. It was found that sintering temperature was lowered, transition width was narrowed, the zero resistance temperature was raised to some degree, and lattice parameters was changed, as the oxygen was substituted by fluorine. It was proved that the fluorine had entered into 123 supercoductive phase lattice. The effect of fluorine on superconductivity was also discussed.