The illegal water injection into meat not only breaks the market equity, but also deteriorates the meat quality and produces harmful substances. In this work, we proposed a fiber Bragg grating (FBG) sensor that enabled fast, quantitative, and in-situ detection of the moisture content of water-injected meat. The FBG was written in the erbium-ytterbium (Er/Yb) co-doped fiber,which could perform the self-photothermal effect by injecting the near infrared laser into the fiber. As the heated fiber sensor probe was inserted into the meat sample, the temperature decreased due to the heat dissipation mediated by moisture. The intracore Bragg grating could monitor the temperature loss by recording the Bragg wavelength shift, which reflected the water content quantitatively. The results revealed that the sensor could complete the detection within 15 s. The sensor’s sensitivity to detect changes in the pork water content was theoretically calculated to be 0.090 847%. The proposed sensor is expected to provide a novel approach for examination of the meat moisture.