The increasing demand for renewable energy is driving the rapid expansion of the offshore wind industry, leading to intensified research on subsea cables. These cables endure combined thermal, electrical, and mechanical stresses, with mechanical stress being a critical failure factor. Environmental changes, such as seabed scouring, free spans, and seismic activity, accelerate cable degradation by introducing additional dynamic loads. Conventional monitoring systems primarily track thermal stress, lacking the ability to assess mechanical impacts. This study develops a system to simultaneously measure thermal and mechanical stress in subsea cables. Laboratory experiments confirm the system’s reliability, showing a temperature measurement error within 0.8% at 60℃ and a strain measurement error within 13% at 378 με. The proposed system aims to enhance failure prediction and maintenance strategies for offshore wind subsea cables.