We successfully designed and fabricated fiber Bragg grating (FBG) earth pressure sensors based on additive manufacturing (i.e., 3D printing) technology by embedding an FBG in a 3D printing model made of carbon fibers for pressure monitoring under different conditions. The systematic calibration experiment and stability test of the pressure sensor prepared by additive manufacturing are carried out. The results indicate a good linear relationship between the wavelength and the change in the pressure loaded on the sensors and show that the sensors show good stability in the 100 loading-unloading cycle tests. The experimental results also show that there is a strong correlation between the infilling density of additive manufacturing and key measurement parameters of the pressure sensors, and that the infilling densities of 20%, 40%, 60%, 80%, and 100% correspond to the sensitivities of FBG earth pressure sensors of 0.69, 0.45, 0.39, 0.21, and 0.19 pm/kPa, respectively. In the field tests, all the seven FBG earth pressure sensors (with a depth interval of 2 m and the sensitivities of 15.38, 0.61, 0.15, 0.76, 0.3, 0.15, and 0.13 pm/kPa) can measure the earth pressure, which is consistent with the theoretical value, indicating good performance of the proposed pressure sensors in actual applications. In conclusion, the proposed earth pressure sensors with an FBG earth pressure sensor encapsulated inside the additive manufacturing model, overcome the shortcomings such as the inflexibility of parameter adjustment for traditional sensors, being susceptible to electromagnetic interference, poor environmental corrosion resistance, complex manufacturing process, inevitable assembly errors, and long R&D and production cycle.