A RIP bushing core dielectric performance test device is set up in order to study the dielectric performance of resin impregnated paper（RIP）bushings at damp condition. On the basis of frequency-domain dielectric spectroscopy（FDS）method

the law of FDS curve variation of the RIP bushing core under the condition of natural damp in the air

drying process and the micro moisture in insulating gas is tested and analyzed. The dampness characteristic parameters and damp diagnostic method for RIP bushings with combination of power frequency dielectric loss factor（tanδ）and the capacitance（C）measurement results are proposed in this paper. Test study result shows that the FDS curve moves to the high frequency direction with the increase of the moisture content and the bushing has the negative tanδ and negative peak in the low frequency band. In case of serious damp

the power frequency dielectric loss factor of the bushing will be significantly increased. The extent of the damp of the epoxy resin impregnated paper bushing in the insulation gas is much lower than that in the air. The variation of tanδ and C at power frequency is very slight. The damp of the bushing can be judged by way of the overall variation rule of tan and FDS curve at 0.1 Hz

which can provide a reference for delivery test and site maintenance of RIP bushing.