The invention discloses a method and a device for detecting an oil mixing interface in sequential oil transportation, belonging to the technical field of oil-gas storage and transportation engineering. A detection device of the invention comprises a V-cone flow sensor, a temperature sensor, a data acquisition module and a computer. The V-cone flow sensor and the temperature sensor are used for obtaining pressure, pressure difference and a temperature signal of a sequential oil transportation section, and concrete position of the oil mixing interface is determined according to pressure difference of one kind of oil having certain density under certain pressure and at temperature, so that accurate cutting of the sequential oil transportation section can be implemented. In the method and thedevice of the invention, the simple V-cone flow sensor, the temperature sensor and the data acquisition module are used for properly solving the problem of mixing oil cutting in the sequential oil transportation through a program set by the computer; simultaneously, the device has the advantages of high measurement accuracy, high degree of automation, low cost, small volume and the like, and can be used for detection of oil mixing interfaces in the sequential oil transportation of industries, such as oil industry, petrochemicals industry, oil field industry and the like.