A four-channel large-capacity, high-speed fiber Bragg grating demodulator is proposed. It constitutes of semiconductor optical amplifier and tunable Fabry-Pérot filter which is composed a high-speed scan laser in a loop structure, combining the optical coupler, optical loop circuit and photodiode. A 2 kHz triangular-like modulation signal is used in this system to drive the Fabry-Pérot filter to make fast scan in the range of 50 nm. The nonlinear effect and scan wavelength shift can be eliminated in Fabry-Pérot filter by introducing the reference channel composed by optical fiber comb filter and single-peak filter, leading to the excellent stability and linearity of demodulator. The stability of high-speed fiber Bragg grating demodulator is 2 pm; the resolution is 1 pm; the linearity is 0.99957; the measuring accuracy is 5 pm, the demodulation frequency is 2 kHz.