In offshore wind farm systems, the submarine cable topology architecture consists primarily of two core components: collector submarine cables and transmission submarine cables, which undertake the functions of power collection and transmission, respectively. For the collector submarine cables, this study established a COMSOL electromagnetic-thermal coupling model to calculate the structural losses and ampacity characteristics of the cable layers under multi-circuit laying conditions. The analysis shows that losses are directly related to wind turbine current and losses in the direct-buriedsection. For the transmission submarine cables, electromagnetic-thermal-fluid multiphysics coupling models were constructed for both direct-buried and J-tube laying conditions. The study systematically investigated the influence mechanisms of ambient temperature, wind speed, and solar radiation intensity on ampacity, and established a multivariate linear regression prediction model for ampacity under environmental constraints in the J-tube section.