Cu2ZnSnS4 (CZTS) thin films have been first in situ grown by reactive magnetron co-sputtering and its characterizations has been carried out by energy dispersive spectroscopy(EDS), X-ray diffraction(XRD), scan electron microscope(SEM), optical transmittance and electronic measurement. It was observed that the grown film shows homogeneous, compact surface morphology, and consists of large columnar grains throughout the thickness. The atom ratio Cu/(Zn+Sn) is about 1, while Zn/Sn is larger than 1 and decreases with the increase of substrate temperature. XRD analysis indicates that the grown film exhibits strong preferential orientation along (112) plane and the structural properties depend on growth temperature and Cu/(Zn+Sn) ratio. The in situ grown CZTS film has an optical absorption coefficient higher than 104 cm-1, and the optical band gap becomes narrow with the increase of substrate temperature and achieves (1.51±0.01)eV at 500℃. The conduction type of the CZTS films is p-type and the value of carrier concentration is comparable with values of device quality CIGS.