Abstract: To investigate the internal deformation law of the coal pillar in the lower section of the legacy coal pillar and its influence on the stability of the roadway, taking 22206 and 22208 working faces of Live Chicken and Rabbit Shaft of Daliuta Coal Mine as the background of the project, theoretical analysis, on-site measurements and numerical simulation wwere used, the distributed fiber optic sensors were implant inside the coal pillar, and finally, a systematic analysis of the internal deformation of the coal pillar in the downward section of the coal pillar was carried out through the fiber-optic strain characterization. The research results show that the strain change monitored by the distributed fiber optic can reflect the internal force of the coal pillar and the range of elastic-plastic region. It is concluded that the elasticity area of coal pillar in the lower section of remaining coal pillar is 62% of that in the hollow area, and the coal pillar is more likely to be destabilized and damaged. The strain growth rate of the distributed fiber optic was used to reflect the drastic destruction of the coal pillar, and it is found that the three stages of the working face mining passing through the area of the remaining coal pillar are entering, passing and exiting the pillar, and it is pointed out that the degree of stress concentration at the stage of exiting the remaining coal pillar was larger than that of entering and passing through the remaining coal pillar. The research results provide a reference for the research of the distributed fiber optic sensing technology used in the monitoring of internal deformation of coal pillars.