A kind of dynamic tracking system for conducting high-precious measurement of transparent liquid concentration is designed. In accordance with the relations between liquid concentration and refractive index as well as the relations among refractive index, interference light wavelength of optical-fiber Fabry-Pérot (F-P) interferometer and grade orders, the liquid concentration variable quantity is obtained by measuring the variable quantity of fringe interference order. In this system, light source is He-Ne laser. Wavelength is 632.8 nm. Output poweris 2 mW. Reflectance of interference cavities is 0.90～0.95, the plane degrees of two reflective surfaces are 1/20～1/100 wavelength, and their parallel degrees are 1/10～1/20 wavelength. Linear charge coupled device (CCD) receives interference frings. When the output signals by linear CCD are processed in two-valuation, the threshold floating measures adopted can eliminate measurement error. The detecting system can recognize or detect concentration variations of 0.01% via measuring a group of alcohol.