Graphene oxide (GO) with different oxygen-containing functional groups was prepared by improved Hummers method, then ultrasonic dispersion. And the graphene oxide film prepared by spin coating method. The type and content of the functional groups, spectral characteristic were implemented by XRD, FT-IR, XPS. Ammonia(NH3) sensitivity is tested by WS-30A gas sensing system. The result shows that graphite oxide contains oxygen functional groups such as hydroxyl group (C-OH), epoxy group (C-O-C) and so on, the maximum spacing of surface network reaches 0.935 nm；with the oxidation degree increases, the initial resistance of the component increases from 550 KΩ to 2500 KΩ. The sensitivity of different GOs gas sensors to NH3 is positively correlated with the relative content of hydroxyl group. When the relative content of hydroxyl group in GOs is 43.75%, the maximum sensitivity of gas sensor to 80 ppm NH3 is up to 78%, and the response time is 37 s, and the gas sensor exhibits good stability and repeatability, the minimum error of repeatability is 3.1%. There are two mechanisms for the response of GOs to NH3 molecules: the ionic conductance mechanism of NH3 molecules entering GOs interlayer water molecules after hydrolysis to form NH4 ions; the charge transfer mechanism of hydrogen bonds formed by oxygen functional groups on the GOs structure layer after adsorbing NH3 molecules.