Understanding the temperature distribution of submarine cables is crucial for ensuring their stable operation, and it is also an essential requirement for the current digital twin analysis of submarine cables. To more rapidly obtain the temperature of submarine cables, this paper proposes a reduced-order computational model based on Proper Orthogonal Decomposition and Polynomial Response Surface Method. Initially, a finite element model of the electro-thermal-flow multiphysics coupling for three-core submarine cables was established. Subsequently, the Proper Orthogonal Decomposition (POD) method was employed to extract modes from the temperature field sample space. A Polynomial Response Surface Model (PRSM) was then utilized to construct a response surface model for the POD modal coefficients, enabling the rapid acquisition of these coefficients under operational conditions and thereby efficiently reconstructing the temperature field of the submarine cables. The reduced-order model proposed in this paper significantly enhances computational efficiency while maintaining high accuracy. Compared to the full-order model, the error in reconstructing the temperature field using the reduced-order model is less than 0.3 °C. The computation time was drastically reduced from 6977 s with the full-order model to just 3.641 s with the reduced-order model.