The invention relates to an oil decanting system for an oil stain boasting and an oil water chamber, which belongs to the field of vessel sewage treatment and environment protection. The oil decanting system of the oil stain boasting and the oil water chamber adopts a hydraulic device and each hydraulic remote value is provided with a tee and double-position electromagnetic valve. The electronic unit controls the tee and double-position electromagnetic valve according to a set parameter in a storage device based on the input signal of an oil-water interface meter and a liquid level meter. When the tee and double-position electromagnetic valve opens the corresponding hydraulic control value, the polluted oil in the hydraulic oil floating on the surface of the oil stain water chamber flows to the oil stain chamber through an oil decanting filter. The oil decanting system has the advantages of low investment, energy saving, stable operation with safety and reliability, as well as a high automatic degree and convenient maintenance and management.