Breakdown faults caused by gas leakage in long-distance high-drop gas-insulated transmission lines (GIL) are difficult to detect accurately due to current fluctuations and environmental influences. To solve the problem of large measurement errors in fiber-optic monitoring of such systems, this paper proposes a new multi-parameter distributed optical fiber monitoring method. Theoretical analysis and finite element simulation are used to study the factors affecting flat optical fibers during vertical installation in GIL, and the fiber laying structure is optimized accordingly. The research results demonstrate that a composite monitoring system employing aluminum alloy and flat optical cables can effectively resolve the key problem of significant measurement deviations caused by multiple influencing factors during the installation of optical fibers in long-distance high-drop pipelines. Furthermore, the system achieves accurate measurement of both temperature and stress through experimental verification.