Atomically thin MoS₂ films have attracted significant attention due to excellent electrical and optical properties. The development of device applications demands the production of large-area thin film which is still an obstacle. In this work we developed a facile method to directly grow large-area MoS₂ thin film on SiO₂ substrate via ambient pressure chemical vapor deposition method. The characterizations by spectroscopy and electron microscopy reveal that the as-grown MoS₂ film is mainly bilayer and trilayer with high quality. Back-gate field-effect transistor based on such MoS₂ thin film shows carrier mobility up to 3.4 cm² V^?1 s^?1 and on/off ratio of 10⁵. The large-area atomically thin MoS₂ prepared in this work has the potential for wide optoelectronic and photonic device applications.