Developing offshore wind power is an important measure to achieve the goal of ‘dual carbon'. DC submarine cables are important devices in offshore wind power transmission projects,and the research on the ampacity of submarine cables plays an important role in promoting the large-scale development of offshore wind power. In recent years,the research on the ampacity of high-voltage DC submarine cables has considered relatively single marine environmental factors，and the limitation of temperature difference of insulation layer has not fully be considered. The article establishes an electric-thermal-current coupling model of the 500 kV DC submarine cable and the seawater system. Under different laying methods for single and bipolar submarine cables,the effects of vertical ocean currents (currents flowing perpendicular to the length direction of the cable) flow velocity,limitation of temperature difference of insulation layer and the the different spacing of the bipolar cables on the ampacity are studied. The results show that considering the temperature difference limitation 20 ℃ of the insulation layer comprehensively has a smaller ampacity compared with the situation only considering the temperature limitation 70 ℃ of the wire core,and direct burial laying has a smaller impact on the ampacity compared to any other laying method. It is also found that the ampacity of bipolar submarine cables increases with the increase of the distance between the two poles. When the flow rate is 0.1 m/s,the vortex have a small improvement effect on the ampacity of the submarine cable. The electric field flips around a temperature difference of 6 ℃ in the insulation layer. The research results can provide important guidance and reference for the selection of laying methods,and even for the prediction or evaluation of ampacity.