The methods for measurement of blood flow contain dilution, electro-magnetism, nuclear magnetic resonance, Doppler etc. The dilution, which includes heat dilution, 131Xe, etc., can not display the moving blood flow in real-time. The expenses of nuclear magnetic resonance expenses are very high. Electromagnetism must be used in the surgical operation. And ultrasound Doppler can not record other parameters of hemodynamics synchronously. This paper brings up a kind of blood flow measuring method with simple operating rules, dependable performance, and low cost to meet the needs in hemodynamic studies. The differential pressure between stay and fluxion points of the tube is produced in proportion to the square of velocity while fluid flows through the tube. We not only measure blood pressure or transfer drug using the detention catheter with double chamber, but also detect the differential pressure related within blood flow. The result of detecting cerebral blood flow (CBF) in clinical setting shows this method can record the diagram of dynamic blood flow and is a valid was of detecting blood flow for hemodynamic studies.