Abstract: At present, Optical Frequency Domain Reflectometry (OFDR) technology has made certain progress in multi-seam stress monitoring, but few studies have applied OFDR to investigate the dynamic evolution of overburden fractures under repeated mining of closely spaced double coal seams. Taking the 360608 working face of Xinji No.1 Mine, China Coal Xinji Energy Co., Ltd. as the engineering background, horizontal and vertical optical fiber networks were deployed in combination with OFDR technology to analyze the differences in optical fiber responses to overburden deformation between the mined and unmined areas of No.8 coal seam during mining of No.6-1 coal seam, thereby revealing the mechanism by which the mined and unmined areas of the upper seam influenced the overburden failure characteristics during lower seam mining. The results showed that: ① after No.8 coal seam was fully mined, the overburden fractures exhibited an "irregular trapezoidal" shape, with caving angles of 48° on the crosscut side and 36° on the stop line side, and a fracture development height of 32.5 cm. ② In the unmined area of No.8 coal seam, the overburden evolved into a typical "voussoir beam" structure during No.6-1 coal seam mining, with a fracture development height of 53 cm and a smooth variation in optical fiber strain (peak ≤55.5 με). ③ In the mined area of No.8 coal seam, repeated mining weakened the overburden structure, increasing the fracture development height to 76.25 cm (23.25 cm higher than in the unmined area) and causing severe fluctuations in optical fiber strain (peak up to 9 987 με). The key stratum breakage induced "stepped" fracture penetration, and both the fracture development height and strain amplitude on the coal-wall side were significantly greater than those on the crosscut side. ④ Field monitoring showed that the fracture development height of the unmined No.8 coal seam was about 53 m, consistent with the similarity simulation results. The study confirmed that the goaf of the upper coal seam enhanced the fracture development height of the lower coal seam by 43.9% and increased the strain magnitude by 3-5 times through stress transfer and structural weakening, providing a theoretical basis for safe multi-seam mining and disaster prevention.