A novel fiber-optic sensor unit by combining fiber-optic white-light interferometry and fiber Bragg gratings is proposed for simultaneous long- and short-gauge strain measurements. A new demodulation scheme based on spectral coherence theory for fiber-optic white-light interferometric sensors is proposed. This makes it possible that two quite different types of sensors in one unit can be simultaneously demodulated in the spectral domain. An experimental sensor unit has been built and tested. The results demonstrated that the spectral demodulation of the sensor unit is readily realized and that the sensor scheme is feasible.