Abstract: Frequency domain dielectric response (FDS) technology is an important method for nondestructive evaluation of transformer oil-paper insulation. The nonlinear change of dielectric properties of oil-paper insulation will affect the accuracy of evaluation, thus it is necessary to study the nonlinear FDS properties of oil-paper insulation. In this paper, several groups of oil-paper insulation samples with different aging and moisture content are prepared in the laboratory conditions. The nonlinear FDS test of oil-paper insulation under different test temperature is carried out. According to the test, when the moisture content of oil paper insulation is lower, the low-frequency dielectric response of oil-paper insulation is negatively correlated with voltage at low test temperature. With the increase of test temperature, the nonlinear changing region moves towards high frequency. The relationship between FDS variation and test excitation amplitude decreases. When the test temperature is high and the moisture content of oil-paper insulation is large, the low-frequency dielectric response of oil-paper insulation shows a new nonlinear law, which is positively correlated with voltage. Both relaxation activation energy and AC conductivity activation energy have a linear relationship with the moisture content in oil-impregnated pressboard. The test excitation amplitude affects the AC conductance activation energy more significantly. To eliminate the influence of test temperature on AC conductivity, the correction function is established to correct the low-frequency AC conductivity of oil-paper insulation at high temperature and high moisture content. Finally, combined with the calculation model of water molecular group mobility established in this paper, the influence of moisture content on the nonlinear change for frequency dielectric response of aging oil-paper insulation is quantitatively calculated, and the law is consistent with the experimental results.