Temperature and stress are easily to cause cracks in concrete bridges and endanger the safety of bridges, but traditional strain measurement methods are difficult to apply on a large scale in actual projects. The weak fiber Bragg grating(wFBG) array strain measurement technology has the advantages of easy networking, high-precision, multiple measurable points, strong reliability, strong anti-interference ability, excellent corrosion resistance, wide measurement range and long-distance measurement. It can be widely promoted in the field of large civil engineering strain measurement. In this paper, first, the relationship between strain and wavelength is determined through wFBG strain-wavelength calibration experiments, and a high-precision large-capacity demodulation system is constructed. Then, the feasibility and superiority of wFBG array strain measurement are verified by strain measurement experiment in T-beam loading and unloading process. Finally, an array of 4118 wFBGs is used to monitor the bridge strain on the Hangzhou Xiasha Bridge.