Abstract: In order to study the evolution process of discharge channel parameters in insulating oil, a diagnostic platform for discharge emission spectrum in insulating oil was built. The typical emission spectrum and time evolution emission spectrum are obtained through experiments. The Stark broadening method and the Boltzmann point method are used to diagnose the time evolution characteristics of electron density and electron temperature of discharge plasma channel in insulating oil. The typical plasma spectra show a strong H_α, C₂ Swan bands and lines emitted by coming from electrodes materials. Compared the discharge current waveform with the time evolution emission spectrum, it can be found that the current intensity is positively correlated with the spectral intensity. The diagnostic results of discharge plasma parameters show that the electron density peaks at 1.12×10¹⁸ cm^–3 at 1~2 μs and stabilizes at 10¹⁷ cm^–3 after 18 μs. The electron temperature fluctuates in the range of 7000~8200 K during the whole discharge process and generally shows an upward trend. According to the parameters diagnosis results, it can be judged that the discharge plasma in insulating oil is in the state of local thermodynamic equilibrium.