A fiber attenuated total reflection (ATR) probe which can provide constant pressure on the contact surface is investigated. The probe can be utilized for infra-red spectrum analysis, e.g., Fourier Transform Infra-red spectrum analyzer. The pressure can be continuously tuned from 9 to 11N and once set the error can be controlled within 1%. Using this probe to measure the absorption spectrum of the samples, the influence from the operators can be eliminated and the measurement error can be controlled within 5%.