Abstract: The steady-state ampacity is an important index to measure the power transmission capacity of high-voltage DC submarine cables. In this paper, an electric-thermal-flow coupling model of ±500 kV DC submarine cables was built by using the COMSOL Multiphysics finite-element analysis software. Based on the control variate method, the effects of dimensional parameters, material thermal conductivity and arrangement on the steady-state ampacity of the submarine cables were studied, which were laid in 3 different sections, including the J-tube section, the cable trench section and the tunnel section. The results show that, in the J-tube section, the steady-state ampacity can be increased by both reducing the wall thickness and increasing the outer diameter of the J-tube. In the cable trench section, the steady-state ampacity gradually decreases with the increase of the depth of the cable trench. However, it can be effectively boosted by increasing the cross-section size of the air domain in the cable trench and increasing the thermal conductivity of the cable trench materials. In the tunnel section, due to the factors such as air convection and heat transfer, the steady-state ampacity reaches its maximum when the submarine cables are arranged horizontally with a space of 900 mm. The tunnel section with the lowest steady-state ampacity is the bottleneck section, which can be improved by adding ventilation equipment.