Based on surface science, adsorption of mineral oil, water, gas products (typified by CO2 and CH4), and acids (typified by formic acid) on meta-aramid insulation paper has been investigated by molecular dynamics simulations. When the adsorption process finishes, the free volume fraction in the crystalline region is very small owing to the stable molecular arrangement of fiber. In addition, the number of pores on the surface of the meta-aramid fiber and the pore size are small, and the stable configuration of hydrogen bonds plays an important role, so it is difficult for the mineral oil and aging products to enter the meta-aramid crystalline region. The irregular arrangement of molecules in the amorphous region means that it is easier for the mineral oil and aging products to enter the amorphous region than the crystalline region, and the influence of these substances on the amorphous region is greater than that on the crystalline region. The order of the adsorption strengths of the four types of aging products on meta-aramid fiber is formic acid>water>CO2>CH4. Therefore, it is necessary to monitor the acid and water contents in transformers with meta-aramid insulation paper as the solid insulation material.