A topology analysis method of transformer insulation is proposed, which considers free relaxation process. This method introduces free relaxation factor βi from microscopic dynamics, based on the return voltage line relaxation parameter information. The branch lines of different dielectric relaxation response information is obtained, and the topological structure of transformer insulation is determined. At the same time, the relationship between more than 30 sets of transformer insulation relaxation parameters and condition assessment are studied. The results show that number of relaxation mechanism number N, average time constant and free relaxation factor βi can reflect insulation status. As the aging degree of transformer oilpaper insulation increasing, the number of relaxation mechanism N and the free relaxation factor βi are increasing, on the contrary, the average time constant is decreasing. In addition, free relaxation factor has a different scale in the deterioration of oil and paper, which can provide a new idea for transformer insulation aging evaluation.