In order to adapt to the seepage pressure monitoring′s need of the mine and the dam,a kind of fiber Bragg grating seepage pressure sensor based on the combination of the piston and the diamond structure was proposed. The piston passes the test pressure to the diamond structure and the diamond structure pulls elastic steel sheet, leading the center wavelength of the fiber Bragg grating bonded on the elastic steel sheet to change. In the 500 kPa test environment, the stress characteristics of the diamond structure were analyzed by using the finite element method when the vertex angle was respectively 90°, 110°, 130° and 150°. According to the simulation parameters, the seepage pressure sensor was developed and pressure calibration test and temperature compensation test were carried out on the sensor. Experimental results show that, the sensitivity of the sensor to the seepage pressure is 2.04 nm/MPa、the fitting degree is 0.997 and the repeatability is 0.9%. The temperature sensitivity of pressure measuring grating is 0.023 33 nm/℃ and 0.021 68 nm/℃ respectively, and the temperature compensation grating is 0.009 916 nm/℃.