The invention discloses an oil immersion transformer oil paper electrical resistivity inversion method based on the bisection method. The inversion method comprises the steps that 1, a finite element model of the insulation structure inside a transformer is built by adopting the finite element method according to the inner structure of the transformer; 2, based on the finite element model, the finite elements are computed using the oil immersed paper electrical resistivity as the independent variable and the stabilized insulation electrical resistance of the whole transformer as the dependent variable, and a model of the numerical relationship between the oil immersed paper electrical resistivity and the stabilized insulation electrical resistance is built; 3, based on the numerical relationship model, inversions are performed on the oil immersed paper electrical resistivity by adopting the bisection method, according to the actual values of the oil and electricity resistivity of the transformer and the stabilized insulation electrical resistance. The oil immersion transformer oil paper electrical resistivity inversion method is high in precision, and the shortcomings of a lot of inconveniences in samplings and the large dispersibility and damages to the insulation structures and the like are overcome.