The effects of external stress on Bi2Te3 nano-films have been investigated by first-principles calculation, including stability, electronic structure, crystal structure, and bond order. It is found that the critical thickness of nano-film is sensitive to the stress in Bi2Te3 nano-film while the band gap is near constant. The critical thickness decreases under tensile stress, whereas it increases under compressive stress. The band gap and band order of Bi2Te3 film has been affected collectively by the surface and internal crystal structures, the contraction ratio between surface bond length of nano-film and the corresponding bond length of bulk decides the band order of Bi2Te3 film.