The invention relates to a differential pressure principle-based slug flow detection method and device. The device is characterized by comprising differential pressure type liquid level transmitters, a horizontal straight pipeline and a signal processor, wherein the differential pressure type liquid level transmitters are electrically connected with the same signal processor respectively. The detection method comprises the following steps: (1) arranging at least two groups of differential pressure type liquid level transmitters on the horizontal straight pipeline; (2) transmitting the liquid level of a fluid which flows through the horizontal straight pipeline to the signal processor; (3) confirming generation of a slug flow; (4) confirming attenuation of the slug flow; (5) calculating the flow speed of a liquid column of the slug flow through the known distance of the two groups of differential pressure type liquid level transmitters; (6) calculating the length of the liquid column according to the generation, the attenuation time interval and the flow speed of the liquid column of the slug flow. According to the method and the device, whether the slug flow occurs in the pipeline can be detected, the length and the flow speed of the liquid column of the slug flow can be detected in the pipeline, and the method and the device can be widely applied to slug flow detection processes of various pipelines.