Superconducting Nb3Sn films have been synthesized via Nb coated on bronze with heat treatment. By changing the annealing time and temperature, the tin concentration in different film is varied. Magnetic moment measurement indicate critical temperature Tc of different Nb3Sn thin film are varies with the composition of Nb-Sn. Considering that high temperature will cause deformation of the bronze substrate, all heat treatment temperatures are not higher than 700℃. The experiment results show that high-temperature heat treatment above 600℃combined with medium-temperature heat treatment near 400℃can achieve high Tc while reducing annealing time.