A stress relief cone plays an essential role in a prefabricated termination for the XLPE cable system. It has been pointed out that precipitates occur on certain parts of the stress relief cone surface under long-term operation, which could lead to a dielectric breakdown. This paper describes the development of two-step numerical calculation programs to understand the appearance process of precipitate on the surface of the stress relief cone. The first step is to estimate the distribution of precipitation occurrence over time, considering several ten-year operations. The second step is to estimate the detailed formation process of precipitates based on the molecular dynamics method. As a result, it is confirmed that the occurrence condition of precipitate led by the developed numerical calculation methods is similar to that obtained at the dismantled stress relief cone.