A case study is conducted on a shield tunnel project in the Pearl River Delta having complex geological conditions to investigate the influence of different geological conditions and grouting effects on the deformation of shield tunnel segments during shield tunneling. Furthermore, tunnel segments at various spatial locations and under different geological conditions are monitored using distributed fiber optic sensing based on optical frequency domain reflectometry, which has significant advantages in spatial resolution and sensing accuracy. The selected ring Nos.1 529 and 1 538 are outside the fracture zone, but ring No. 1 551 is inside the fracture zone; moreover, the sensing optical fiber is arranged along the longitudinal reinforcement of the tunnel segment reinforcement cage. The results reveal the following: (1) Grouting has a significant effect on the deformation of tunnel segments, and deformation after synchronous grouting is three times that after secondary grouting. (2) The deformation of segments varies under various geological conditions, and it is relatively large and unstable in the fracture zone compared with that outside; When the tunnel segments enter the complete rock stratum, the deformation of segments is relatively stable. (3) The deformation of segments in the fracture zone is 2.6 times that outside the fracture zone.