We developed a flow visualization system based on laser Doppler velocimetry (LDV) to investigate the relationship between blood flow and blood coagulation in a blood chamber in an extracorporeal circulation circuit. Linear laser intersection was used to implement 32-point simultaneous measurement. The intersection region was traversed along the axial direction to obtain a two-dimensional (2D) velocity distribution as a contour graph. The optical assembly of the flow visualization system is very simple. Furthermore, there is no need to submerge the measurement object in a square water tank to reduce the influence of refraction and reflection. Because LDV has inherently high measurement accuracy, even slight flow velocity changes (less than 1 mm s −1 ) can be clearly identified in a blood chamber.