The thermo-induced nonlinearity of piezo-electrical transducer (PZT) driven fiber Fabry-Perot (FFP) filter using fiber Bragg grating (FBG) sensing system is investigated and evaluated. Polynomial fitting is adopted to model the nonlinearity. Under 4th or higher order polynomial fitting and a reference FBG, the thermo-induced strain error is reduced from 750 με to 15 με and the standard deviation is kept below 10 με while PZT driven FFP experiences over 15 ℃ temperature change. It is observed that thermal effect on PZT driven FFP is not simply invariable or linear in a wide temperature range.