A post insulator includes an insulating post including a first end and a second end that are opposite to each other, a high-voltage-end grading ring connected to the first end of the insulating post, the high-voltage-end grading ring being insulated from the insulating post, a grounding-end grading ring connected to the second end of the insulating post, the grounding-end grading ring being insulated from the insulating post, and a charge control ring disposed on an outer surface of the insulating post, the charge control ring being insulated from the insulating post, and the charge control ring being configured to accumulate surface charges.