Special optical fibers such as elliptical core polarization maintaining fibers, radiation resistant fibers, and erbium-doped fibers are more susceptible to harsh environments such as high and low temperatures in practical applications due to their unique application scenarios. Strict environmental testing is required before application, and optical fibers with mismatched coating geometries are prone to separation defects in practical applications or after environmental testing. This article theoretically analyzes the functional relationship between the maximum shear force required for fiber coating separation and the shear strength of the coating, and determines that the main causes of coating delamination defects are the mismatch in the ratio between the inner and outer coatings of the fiber and the large range of environmental temperature changes. This article verifies the influence of different thickness ratios of inner and outer coatings on the shear strength and delamination defects of optical fibers through coating peeling tests and temperature cycling tests, which is consistent with the theoretical analysis results. The research results of this article have certain guiding significance for optimizing the geometric structure of optical fiber coatings and improving the mechanical reliability of optical fibers.