First-principles calculations are performed to investigate the electronic structure of the Bi2Se3 single-QL thin film and the films doped with Pb. Their band structures and densities of states are explored. The results show that the main composition of the valence band and conduction band of these films is p-states, and their band-gap type can change from the direct to the indirect as Bi2Se3 from block to film. In BiPbSe3 film, The newly appeared Se(1／) layer caused by the doped Pb has an significant impact on the electronic structures of the film, but in the Pb0.25Bi1.75Se3 thin film with the concentration of Pb ～5%, there is the similar band structure to the pristine film. This paper also discusses the modulation of Bi 6s orbital states at the valence band maximum and the concentration of carriers in doped films.