Fused deposition modelling (FDM) has been widely used in the field of sensor production, however, sensor fabricated adopting FDM in monitoring water pressure is seldomly discussed. In this study, one Fiber Bragg Grating (FBG) water content sensor has been designed and fabricated in order to monitor the variation of water pressure at the field. It's worth noting that the advanced material, Polylactic Acid (PLA), has been used in fabricating sensor with favorable stability. After the fabrication of FBG sensor, calibration test was conducted by controlling and measuring water content of soil sample in a sealed chamber through manipulating pressure volume controller. It has been validated that this pressure sensor adopting FDM fabrication process has quick response and high sensitivity. Afterwards, field application of this type of sensors have been used in measuring the variation of soil water content continuously, while reading from different depth of this sensor can be compared and analyzed to summarize the influence of nature rainfall condition about the ground. To validate and verify the reliability and authenticity of developed FBG sensors, the conventional sensors have been implanted at the same depth of FBG sensors and comparison have been conducted in the entire monitoring period. It has been verified that FBG sensors have good performance when embedded into the melted PLA material, while its application in measuring soil water pressure is more sensitive and accurate.