Abstract: At present, the research on the insulation breakdown characteristics of micro-arc oxidation ceramic film is mostly focused on the impact of changing the process parameters. The insulation characteristics of ceramic film in different growth processes are not clear yet. Therefore, this paper investigates the change rule and internal mechanism of the power frequency breakdown characteristics of ceramic film growth process. Firstly, the ceramic insulation wire samples with different oxidation times were prepared. Secondly, the surface and cross-section morphology, elemental distribution, phase composition and other microscopic features of the ceramic film were analyzed. Further, the two-parameter Weibull distribution method was used to obtain the variation rule of the power frequency breakdown voltage of the ceramic film with the oxidation time. Finally, the key factors and internal mechanisms affecting the breakdown characteristics were analyzed. The results show that the power frequency breakdown voltage during the growth of ceramic film shows a nonlinear trend. The rising rate can be divided into four intervals with alternating fast and slow speeds, the oxidation time is determined to be 2~6 min, 6~14 min, 14~18 min, and 18~30 min intervals, and the rate of increase of the power frequency breakdown voltage is 17.91 V/min, 8.43 V/min, 25.38 V/min, and 8.60 V/min, respectively. The thickening of the ceramic film and the phase transition of Al₂O₃ are the major factors for the increase of the power frequency breakdown voltage. During the growth process, the thickness and roughness show a linear increase trend, with the growth rate of 2.32 μm/min and 0.15 μm/min, respectively. The density of the ceramic film shows a decreasing trend from 1.46 g/cm³ to 0.05 g/cm³. When the oxidation time is 16 min, the α-Al₂O₃ crystalline phase appears in the film and the mass fraction of α-Al₂O₃ is gradually increased with the growth of the oxidation time, and the maximum is 21.37%. Because the power frequency breakdown field strength is an average value and reflects the average strength of the ceramic film. With the increase of oxidation time, the power frequency breakdown field strength shows a decrease trend, from 34.25 V/μm to 7.33 V/μm. The inhomogeneous characteristics of the microstructure and material composition of the ceramic film are the key factors influencing the change of the power frequency breakdown characteristics.