The invention provides an oil-water separator. The oil-water separator is composed of components of a pump, a switching valve, a tank, an aerating device, a pressure detecting and releasing port, an oil collection device, a water purification film device, an oil-water pipeline, a bottom pipeline, a water separation pipeline, a top pipeline and a purification oil film device. The oil-water separator is small in size, and a main body of the oil-water separator is only composed of the tank and parts of the components; the efficiency of the oil-water separator is high, processing time of the oil-water separator is shorter than that of multi-stage stationary devices, and oil can be continuously discharged tens of minutes later; and various oil-water mixtures, petroleum-seawater mixtures, catering oil-water mixtures and the like can be treated, and discharged water reaches national emission standards according to different requirements. The oil-water separator is reasonable in design, simple and convenient in production process, convenient to operate, suitable for being used in small-size steamers and fishing boats, and applicable to oil-water separation on land and oil-water separation of petroleum, machine oil, kitchen oil and the like, separated oil can be recycled so that economic benefits are increased, and separated water can be recycled so that water resources are saved.