The function of components and the theory of oil-paper capacitive bushing are introduced by analyzing its contracture, and the electric properties of insulation materials are instructed. The reasons and damages of lack of oil are proper illustrated, and the judging methods are offered. The distinguishing process of lack oil of bushing is illustrated by examples, and the accuracy and rationality of lack of oil finding by capacitive volume, dielectric loss angle, oil chromatogram analyzing and infrared ray test are demonstrated. Introduction The bushing is a kind of widespread used electrical equipment in power system. With a bushing the high voltage lead wire can pass through the earth body (wall, metal partition board and so on) or the oil box cover of electrical equipment to connect to other equipments. The transformer bushing and the wall bushing are used frequently for insulation and wire supporting in power system. The oil-paper capacitive bushing has been widely used in 66kV and upper voltage system because of its high utilizing factor of insulation, large specific capacitance, reasonable structure and small volume. In the long-term operation, the bushing have to bear the highest working voltage of long-term but also withstand all kinds of possible over-voltage, while the bushing itself due to dielectric (cable paper, transformer oil) gradual deterioration, moisture and partial discharges and other reasons, susceptible to various accidents. Ingress of moisture which will make the bushing oil lacking, resulting in insulation damp, will lead to partial discharge occurred within the bushing, causing the explosion [1]. Structure of oil-paper capacitive bushing Fig. 1 Structure of oil-paper capacitive bushing Oil-paper capacitive bushing consists of the copper conductive tube (pole), oil impregnated paper condenser cores, ceramic or compound hollow insulator and accessories [2]. The structure of 5th International Conference on Machinery, Materials and Computing Technology (ICMMCT 2017) Copyright © 2017, the Authors. Published by Atlantis Press. This is an open access article under the CC BY-NC license (http://creativecommons.org/licenses/by-nc/4.0/). Advances in Engineering, volume 126