Research work has been done in optical fiber sensor demodulation system based on broadband light source. Multi-FBGs are used as wavelength reference and fiber Fabry-Pérot tunable filter (FFP-TF) is used as wavelength selection device in the system. A non linear fitting based on cubic polynomial is adopted as the best fitting algorithm to convert scanned voltage of FFP-TF sawtooth wave to scanned transmission wavelength, which can solve the systemic error caused by the non linear relation between the wavelength and scanning voltage of FFP-TF, and then get higher demodulation resolution. In the experiment, five reference FBGs are used in the demodulation system. One FBG sensor demodulation result shows that wavelength resolution of measurement FBG is 3.5 pm for a short time, and long-term stability is 7 pm. An EFPI optical fiber strain sensor is tested with the demodulation system, which shows the strain sensitivity of 2.41 nm/με, besides, there is good linear relation between strain and wavelength with a linear correlation coefficient of 0.99991.