The invention discloses a fiber grating sensor demodulating system which comprises N light source groups, a first optical fiber combiner, a first optical fiber shunt, a first photoelectric detector, a first signal amplifier, a data collecting card, a computer, K circulators/couplers, photoelectric detectors corresponding to every circulator/coupler and signal amplifiers. An Nth light source group comprises MN light sources; when MN>1, every light source in the light source group is connected to the first optical fiber combiner through a second optical fiber combiner, and one scanning filter is further arranged between every light source group and the first optical fiber combiner; when K>1, the fiber grating sensor demodulating system further comprises a second optical fiber shunt, and every circulator/coupler is connected with the first optical fiber shunt through the second optical fiber shunt. Through the fiber grating sensor demodulating system, measuring bandwidth and measuring precision can be improved, and the quantity of measurable fiber grating sensors can be increased.