Abstract: Direct burial is one of the common laying forms of submarine cables. Discrepancies in boundary condition settings can greatly affect the calculation results of current-carrying capacity. Currently, no unified specification has been formulated for COMSOL simulation modeling of submarine cables in China, and modeling parameters are selected in a relatively arbitrary manner. This paper takes submarine cables buried in air and seabed as the research object. Comparative analysis is carried out by means of COMSOL finite element simulation. Three types of boundary conditions are studied to explore their influence laws on cable current-carrying capacity, including the distance of rectangular lateral thermal insulation boundary under direct burial, two setting modes of upper boundary (constant temperature and heat flux), and the spacing between cables and constant-temperature lower boundary. The research results show that the reasonable range of lateral thermal insulation boundary distance is 10~15 m. Heat flux boundary is applicable to the upper boundary under direct burial working conditions, and the optimal spacing between cables and constant-temperature lower boundary is controlled within 10~12 m. This study clarifies the standardized selection basis of boundary conditions for directly buried submarine cable simulation, and effectively avoids calculation errors arising from inconsistent modeling parameters. It can provide references for the construction of standardized COMSOL simulation modeling system for domestic submarine cables, and also offer reliable technical support for engineering design and operational current-carrying capacity verification of submarine cables.