With the increasing demand for submarine cable transmission, the application of J-type conduit structure in laying submarine cables at the landing section has received widespread attention. This article takes a typical 110 kV three-core AC submarine cable as the research object, using COMSOL finite element analysis software to study the impact of J-type conduit diameter and pipe wall thickness on the current carrying capacity of the submarine cable under different laying environments by building an electromagnetic-thermal-fluid multi physics coupling model for the J-type conduit and cable. The heat dissipation of the cable is considered to be divided into three types: thermal conduction between the submarine cable and the air, seawater, and silt water inside the J-type conduit; thermal conduction between the J-type conduit and the external soil; convection heat transfer between the pipeline and the external seawater; and thermal radiation from the air medium inside the pipeline Research indicates that regardless of the pipeline diameter, medium type, or laying environment, the current-carrying capacity of submarine cables decreases as the pipe wall thickness increases; The influence of the diameter of J-type conduit on the current carrying capacity of submarine cable is closely related to the type of medium between pipeline and submarine cable; When the external part of J-type conduit is seawater, the cable has better heat dissipation effect and higher steady-state current carrying capacity. However, in soil environment, the heat dissipation effect is poor, resulting in a decrease in current carrying capacity.