Abstract: In order to apply the Xray direct digital imaging technology to the field of nondestructive testing of the transformer, it is necessary to determine whether there exists impact of Xray irradiating on the insulating oil. This paper proposed a research of using Xray to irradiate the transformer oil. The concrete content of the study is to irradiate the applied voltage for given energy and given time by portable high frequency Xray generator. Experimental results show that Xray has little effect on the gas component of transformer oil. This study will provide clear and adequate basis for applying the Xray direct digital imaging technology to the field of nondestructive testing of oil filled electric equipment and it will offer technical support for application of electrical equipment based on digital Xray imaging system as well.