By using white light fiber optic Michelson interferometer, the temperature and strain coefficients of fiber optic refractive index were determined via the measurements of optical path changing as a function of temperature or strain. The results shown that the temperature and strain coefficients of fiber optic refractive index were 0.762×10 -5 /℃ and -0.1332×10 -6 /με for 1300 nm wavelength and 0.811×10 -5 /℃ and -0.1649×10 -6 /με for 1550 nm for the type SMF 28 single mode communication optical fiber, respectively. The measured results were compared with published data.