Cu2ZnSnS4 (CZTS) films with a smooth and compact morphology were obtained via a sol-gel process. Raman spectra and X-ray diffraction (XRD) results indicate that all the films have the kesterite structure. Energy dispersive X-ray spectroscopy (EDS) suggests that all of CZTS films are of S-deficient, Cu-poor and Zn-rich states. The thickness of all the films is around 0.7μm measured by a field emission scanning electron microscope (FE-SEM). Transmission spectra reveal that the optical band gap (Eg) of samples reduces from 2.13 to 1.52eV as post-annealing temperature goes up.