The invention provides a drilling fluid flow detection device and method. An inlet flow detection device probe of the device detects the fluid flow velocity of a drilling fluid inlet pipeline and an outlet flow detection device probe detects the fluid flow velocity of a drilling fluid outlet pipeline; an ultrasonic wave distance measuring device measures the height of a fluid surface of the drilling fluid outlet pipeline; an inlet flow data collection and processing module performs signal processing on the fluid flow velocity data of the drilling fluid inlet pipeline, and the outlet flow data collection and processing module performs signal processing on the fluid flow velocity data of the drilling fluid outlet pipeline and the height data of the fluid surface of the drilling fluid outlet pipeline; a logging unit data collection system transmits signals output by the same to an underground complicated condition analysis system which performs data storage, display, playback and analysis. The drilling fluid flow detection device can realize real-time quantitative detection and analysis for drilling fluid inlet and outlet and has remarkable economic benefit and social benefit for oil-gas exploration.