To essentially eliminate the measurement errors arisen from light source power fluctuation, a measurement method of solution concentration was proposed. The method is based on the relationship between transmission optical spectrum central wavelength of fiber Fabry-Perot (FFP) interferometer and the refractive index of medium in the cavity, as well as the relationship between solution refractive index and its concentration. Such a measurement system was developed. A tunable fiber optical Fabry-Perot (F-P) filter was used to collect the sensing data. Different concentrations of a set of alcohol solution, with the concentration being from 5% to 80%, were measured experimentally. The maximum absolute measurement bias is no more than 0.003%. This measurement system possesses following advantages