A field-programmable gate array (FPGA)-based large-capacity sensing network with ultra-weak fiber Bragg gratings (FBGs) is proposed and experimentally studied. The demodulation system is constructed to interrogate 1642 serial time-division-multiplexing FBGs with a peak reflectivity of about 40 dB and equal separations of 2.5 m. Two semiconductor optical amplifiers and an InGaAs linear sensor array controlled by an FPGA are introduced to the demodulation system to achieve fast, precise, and flexible interrogation. The low crosstalk and spectral distortion are investigated through both theoretical analysis and experiments.