The simulation of DC ageing evolution in insulating polymers is of an important significance in promoting the development of computational high voltage engineering（CHVE） both for theoretical understanding and practical application. We propose a numerical model of ageing with the finite difference grid in the two-dimension coordinate which is programmed by using MATLAB. The material inhomogeneity of large-size samples is characterized by generic features assigned to small-size elements based on fitting parameters obtained from life data of thin films. The quantitative simulations of ageing are carried out by using the chemical reaction rate theory to calculate theageing process. It was found that micro degradation occurs in weak spots at the early stage causing local electric field distortion. The local field enhancement further accelerates the local ageing process which leads to the growth and extension of degraded regions. Once the local field reaches the critical value

the final breakdown occurs to form a filamentary conducting path linking the two electrodes with a small volume of fractal structure due to the field divergence when approaching the electrode. The proposed simulation is efficient and visualized to reflect the physical pattern leading from stochastic micro degradation to deterministic macro failure in the ageing process of polymeric insulation

which provides theoretical reference and basis for in-depth understanding of ageing failure.