We designed a new module of Laser Doppler Anemometry (LDA) with fiber optical system, which is mainly comprised of a laser diode, optical fibers and a two dimensional (2D) photodetector. The fiber optical system involved a laser diode (VCSEL, Copax Inc.) with 850 nm wavelength, single mode fiber (Prime Optical Fiber Inc.), half coupler and two fiber collimators. The 2D photodetector made by silicon PIN photodiode is aligned between the two collimators with 39° beams cross angle and all the components were set into a rectangle case, which have coin’s size and can be accommodated by two same set of these components. We added anticoagulant and antiseptic into fresh chicken blood and diluted it with normal saline, and then put the diluted blood into a beaker with a motor in the liquid. The diluted blood was pumped by the motor into an aqueduct which is connected to glass aqueduct, and back to the beaker to form a circulation system. In the experiments, we evaluate the relationships among the blood cell velocity and diameter of glass tube, temperature variation of blood, and concentrations of blood. By analyzing the results of these experiments, the main factor that affects the precision of velocity measurement is the cross angle of two injected laser beams and the intensity of scattering light. The module constructed by optical fiber light can precisely measure the velocity of blood flow at most 5% error.