The development of electric energy is closely related to the development of the national economy, so the stable and safe operation of the power grid guarantees the people’s stable life. The stable and reliable operation of the power grid is related to the insulation level of the transformer, so it is very important to always pay attention to the condition and operation of electrical equipment. The furfural produced only by paper insulation is currently one of the most commonly used indicators for evaluating the aging status of power transformers, so it is of great significance to accurately measure the furfural content in transformer oil. Raman spectroscopy based on the Raman effect can achieve rapid and non-destructive detection of the object to be tested, but limited by the weak Raman scattering signal, it is not easy to detect trace substances such as aging characteristics in oil. Surface-enhanced Raman spectroscopy technology can solve the sensitivity problem of trace substance detection and enable fast and non-destructive detection of aging features dissolved in transformer oil. Therefore, the application of SERS to detect furfural in transformer oil is of great significance for evaluating transformer operating conditions. In this article, around the problem of low detection sensitivity of furfural in transformer oil as a trace substance, a micro-nano structure SERS substrate was prepared on the TEM copper mesh based on the displacement reaction to detect furfural in transformer oil. It provides a fast and effective new method for efficiently and accurately detecting the aging level of transformer oil. In this paper, specific experimental materials are selected, the micro-nano structure SERS substrate is prepared based on the displacement reaction under controlled specific experimental conditions, and its surface morphology is characterized by scanning electron microscopy. Raman characteristics are obtained by Raman detection at different detection positions The relative standard deviation of peak-to-peak intensity is only 3.55%, indicating that the substrate has a uniform distribution of “hot spots” and higher detection repeatability; qualitative analysis of the Raman spectra of furfural in transformer oil with a certain concentration gradient and the Raman of the background noise spectrum. Combined with the selection rule of Raman characteristic peak, the Raman peak of 1 702 cm^-1 was selected as the Raman characteristic peak of furfural in oil. In the quantitative analysis, a linear function of the ratio of the standard internal peak to the peak at 1 702 cm^-1 and the furfural concentration in the transformer oil was established, and it was concluded that it has a good linear relationship. The 3δ principle is used to calculate the minimum detection concentration of furfural in transformer oil on the micro-nano structure SERS substrate, which is about 0.51 mg·L^-1. In this paper, the micro-nano structure SERS substrate based on copper mesh displacement reaction has a more sensitive detection of furfural in transformer oil. This is very important for diagnosing the insulation status of power transformers and maintaining the stability of the power grid.