This paper discusses the possibility of using nanocrystalline ZnO films as photo_electrode in dye_sensitized solar cells (DSCs). The performances and mechanism of DSCs based on ZnO nanoporous film are observed by using IR, UV_vis spectra and LSV method, and compared with dye_sensitized solar cells based on nanocrystalline TiO2 films. It is found that the low efficiency of DSCs based on ZnO is due to the poor binding force between the surface of nanocrystalline ZnO films and the RuL2(NCS)2(L=2,2′_bipydyl_4,4′_dicarboxylate) dye.