The second harmonic content is one of the main characteristics of transformer inrush current. For a transformer, the closing angle, the core flux saturation point, the transformer capacity, the transformer structure and the transformer voltage grade are certain, but the remanence is the only uncertain factor. Based on the discrete data simulated by the model established by Matlab, the higher order nonlinear interpolation function is obtained by Lagrange interpolation method, and the graph of the function is drawn, boundary Range for evaluating the second harmonic content of transformer inrush current under the influence of remanence. Based on a case study, this paper proves the practicability and effectiveness of the method.