The invention discloses a piece of power-frequency voltage-withstand testing equipment and method for a composite post insulator. The equipment comprises a frequency converter, an excitation transformer, a lightning rod, a resonance reactor, a high-voltage test conducting wire, a voltage divider, a parallel reactor, a test article and a grounded copper strip, wherein the frequency converter, the excitation transformer and the lightning rod are connected in sequence; the resonance reactor and the high-voltage test conducting wire are connected with the lightning rod and a first common terminal of the excitation transformer in sequence; a high-voltage terminal of the voltage divider is connected with a high-voltage terminal of the high-voltage test conducting wire; the grounded copper strip is connected with the lightning rod, a second common terminal of the excitation transformer, a low-voltage terminal of the voltage divider, a low-voltage terminal of the parallel reactor and a low-voltage terminal of the test article; the grounded copper strip is grounded. The power-frequency voltage-withstand testing equipment and method for the composite post insulator can overcome the defects that in the prior art, flaw detection can not be carried out, the detection difficulty is high and the like and achieve the advantages of easiness in flaw detection and convenience in detection.