According to the model of the superconducting proximity effect between a nonsimple metal thin film with negative U centers and a thin film of BCS superconductor, we have discussed the gap functions, the electronic density of states and the transition temperature Tc varying with different parameters. Results show that a small density of states due to the -U centers exists in the region of "energy gap". The transition temperature of this kind of sandwich is probably higher than the Tc of the bulk BCS superconductor within certain range of parameters.