The application provides a non-destructive moisture detection device and method in insulating oil. The device comprises a terahertz wave generating component, a sample testing component, a data processing component and a supporting computer. In addition, the method includes the following steps that: a database is established; and sample testing is carried out. On the principle of having the largedifference between the metallic material, the non-polar material, and the polar material by the terahertz wave, the moisture content in insulating oil is detected on the premise that no chemical agentneeds to be added. The information of the water content in the insulating oil is shown by the amplitude difference of the terahertz wave. After the amplification process, the non-destructive moisturedetection method enables the error of generating the blank current in titration by the interference according to the coulometric titration method by being compared with the traditional coulometric titration method, so that the measurement accuracy is improved. After sample measurement, the sample hardly changes; and the measured sample can be recycled and non-destructive testing is realized.