Abstract: In order to address the problems of space charge accumulation, electric field distortion, and imperfect multi-physical field coupling simulation system in the insulation design of medium-voltage direct current (MVDC) cables, this paper adopts the finite element method (FEM) to construct a two-dimensional axisymmetric electro-thermal coupling model. Taking 10kV DC cables as the research object, the physical field distribution of the cables under DC steady state, operational and lightning impulse voltages is systematically simulated by changing the thickness of XLPE insulation layer and the thickness combination of conductor shielding and insulation shielding. The results indicate that the optimized design with a thick inner shield and thin outer shield combined with differentiated insulation thickness arrangement is beneficial to ameliorate the electric field distribution in insulation. This work provides reliable simulation methods and data support for the refined design and engineering application of MVDC cable insulation systems, and helps improve the operational reliability of cables in the DC transformation of distribution networks.