Researchers are already becoming willing to get involved in bismuth oxysulfide (Bi₂O₂S), a new two-dimensional optoelectronic material with a lengthy carrier lifetime and a unique loose structure. In this work, the Bi₂O₂S nanosheets are produced by room temperature chemical synthesis and built a Bi₂O₂S nanosheets flexible photodetector based on deionized water solid-state electrolytes. Photoelectrochemical tests showed that the photodetector based on deionized water solid-state electrolyte had excellent photoresponse performance under 0 V, and its photocurrent density was 0.55 μA/cm² when the optical power was 75 mW/cm². In addition, the photodetector exhibited superb stability. After cycling the “on–off” behavior for 1000 s, the photocurrent slightly decreased 8% than initial state. At a bending angle of 30°, the photocurrent density was about 91% of the original state, but when the bending angle is 60°, the photocurrent density was about 76% of the original state, which may be caused by the small cracks formed during the bending process. The results showed that the flexible photodetector based on Bi₂O₂S nanosheets had decent stability and mechanical flexibility, and were safer and more environmentally friendly than traditional detectors, providing a workable option for the flexible photodetector’s construction.