The invention provides a product oil sequential transport pipeline mixed oil interface tracing method and device. The product oil sequential transport pipeline mixed oil interface tracing method comprises the steps that characteristic parameters of a pipe section are obtained in real time; the characteristic parameters comprise first data pairs which comprise the upstream pressure head measuring value, the upstream flow measuring value, the downstream pressure head measuring value and the downstream flow measuring value of the pipe section at the current time; on the basis of multiple second data pairs generated at random, the multiple third data pairs are generated, the second data pairs comprise the mixed oil center interface position random value and the mixed oil length random value of the pipe section at the current time, and the third data pairs comprise the upstream pressure head calculation value and the downstream pressure head calculation value of the pipe section at the current time; and the third data pairs with the values forming deviation meeting the preset condition with the corresponding values in the first data pairs are determined, and the corresponding random values of the determined third data pairs are determined to be the mixed oil center interface prediction value and the mixed oil length prediction value of the pipe section at the current time correspondingly. Through the product oil sequential transport pipeline mixed oil interface tracing method and device, the accuracy of product oil sequential transport pipeline mixed oil interface tracing can be improved.