The behavior of soil-geogrid interaction is a dominant factor in the long-term performance of geogrid-reinforced earth structures. This study investigates the interaction of sandy soil and the embedded geogrid by pullout tests with the application of a novel testing method using fiber Bragg grating (FBG) sensors. Three influencing parameters are considered: dry density of soil, initial normal stress, and fixing condition of the pullout back end. A displacement-controlled mode is used for the normal stress, and the pullout load is applied at a constant loading rate. The results indicate that for the case with a free back end, the peak shear stress mobilizes from the front face toward the back end with the elongation of the geogrid during the pullout process, before the entire slippage of the geogrid. With higher dry density or higher initial normal stress, the mobilization of the peak shear stress transmits more slowly and the distribution area of shear stress along the geogrid is accordingly narrower due to the corresponding higher resistance by the soil particles. However, the values of the peak shear stress in these two cases are still higher than in cases with lower dry density or lower initial normal stress. By contrast, a different distribution mode of shear stress along the soil-geogrid interface is identified for geogrid with a fixed back end, with maximum shear stress developing near the front face for all pullout displacements.