Mineral oil in the power transformer has an important role in the cooling, insulation aging and chemical reactions such as oxidation. Oil temperature increases will cause quality loss. The oil should be regularly control in necessary time. Studies have been done on power transformers oils that are used in different age in Iranian power grid to identify the true relationship between age and other characteristics of power transformer oil. In this paper the first method to estimate the life of power transformer insulation (oil) is based on Arrhenius law. The Arrhenius law can provide loss of power transformer oil quality and estimates remaining life. The second method that is studies to estimate the life of power transformer is the paper insulation life prediction at temperature160 ° C.