The invention provides a porcelain insulator internal insulation detection method and a porcelain insulator detection circuit, and the method comprises the steps: S101, transmitting an impact voltagethrough an impact voltage generator, and obtaining voltage change waveform data through a measurement loop; S102, acquiring a first voltage amplitude, a first attenuation time constant, a second voltage amplitude and a second attenuation time constant according to the voltage change waveform data; S103, acquiring the insulation resistance of the porcelain insulator to be detected according to thefirst attenuation time constant and the second attenuation time constant; and S104, judging whether the porcelain insulator to be detected is a deteriorated porcelain insulator or not according to thefirst voltage amplitude and the second voltage amplitude or the insulation resistance of the normal porcelain insulator and the insulation resistance of the porcelain insulator to be detected. The method is high in accuracy, can quickly detect the porcelain insulator with internal insulation degradation, is short in pressurization time, is low in power, is low in energy consumption, is simple injudgment logic, facilitates the integration, facilitates the miniaturization of detection equipment, and is wide in application range.