The invention discloses a method for obtaining the tree sapwood width based on a resistivity method. The problem during acquisition of the tree sapwood width is solved. The method specifically includes following steps: step 1, making an apparent resistivity acquisition determination scheme, and acquiring apparent resistivity data of a trunk; step 2, performing inversion imaging calculation on theacquired apparent resistivity data, obtaining resistivity data of the cross section of the trunk and generating a resistivity imaging image; step 3, extracting a resistivity value along the diameter direction of the trunk from the resistivity data of the cross section of the trunk, and establishing a resistivity-distance relation diagram; step 4, performing curve fitting on the resistivity-distance relation diagram, and obtaining a change curve of a smooth resistivity with the distance; and step 5, taking a natural logarithm for the change curve of the resistivity with the distance, obtaininga turning point of the change of the resistivity, and recording the distance corresponding to the turning point. According to the method, the determination is simple, the calculation is convenient, the damage to trees is avoided, results are reliable, and the feasibility is high.