A method for measuring liquid volatilization by using fiber loop ring-down technique incorporating an etched fiber was analyzed and experimentally demonstrated. The transmissivity of the single mode fiber were deduced according to the coupled-mode theory; the energy distribution over the cross section of the fiber was numerically analyzed by using the finite element method. The results showed that, thinner the diameter of the single mode fiber, larger would be the extinction coefficient, thus leading to more energy loss in the fiber core. The etched fiber with length of 1 cm and diameter of 26 μm was chosen through analyzing. Through the relationship between ring-down time and concentration of ethanol, the changement of ethanol′s concentration in ethanol-glycerol solution was obtained during volatilization at 30℃. The experimental results show that the concentration of ethanol decreases exponentially with the time which is in good agreement with the theoretical derivation. Since the refractive index of liquid which varies linearly with the concentration increases with the volatilization of ethanol, leading to stronger evanescent wave absorption, as a result, the ring-down time decreases. In addition, this method has very low temperature cross-sensitivity.