A fiber Bragg grating (FBG) soil-pressure sensor based on dual L-shaped levers is proposed and demonstrated. Using dual L-shaped levers, the deformation of the diaphragm, which experiences the soil pressure, will be transferred to the longitudinal strain of the FBG. The theoretical analysis on the sensitivity of the proposed sensor is given. The sensor has been calibrated in the laboratory. Experimental results show a good agreement with theoretical expectations. Furthermore, this soil-pressure sensor has been installed in an earth dam in Beijing, China. Drifting of the FBG wavelength has been collected in rainy days from May to July 2012. It has been found that the earth dam has an obvious change of internal stress in the rainstorm.