In this paper, a polarization maintaining fiber (PMF) is used as the sensing element for microfluidic velocity measurement. The proposed fiber microfluidic velocity sensor adopts the Sagnac loop structure, where the PMF is incorporated in the fiber loop. The microfluidic velocity measurement is realized by monitoring the output spectrum of the Sagnac loop. Different microfluidic velocity causes different pressure on the side of the PMF, which leads to the wavelength shift of the output spectrum of the Sagnac loop. Experimental results show that a quadratic relationship between the microfluidic velocity and the dip shift of the output spectrum has been observed with the microfluidic velocity range from 0∼900um/min. The proposed microfluidic velocity fiber sensor owns significant behavior in various applications such as chemical engineering and medical equipment technology.