The invention discloses a transformer bushing tap insulation test sub-control device which comprises a transformer sub-control electrode module and an insulation resistance meter. The transformer sub-control electrode module comprises a frame, a plurality of fixed contacts, a sliding table and a driving mechanism, the fixed contacts are fixed onto the frame, the sliding table is slidably arrangedin the frame, the driving mechanism drives the sliding table to move in a reciprocating manner, and three movable contacts are arranged on the sliding table. During test, the first movable contact andthe third movable contact are grounded through leads, the second movable contact is connected with an L binding post in the insulation resistance meter through a lead, an E binding post in the insulation resistance meter is grounded through a lead, and the fixed contacts are connected with a bushing tap in a transformer to be tested through leads. When in test, the sliding table moves by the aidof the driving mechanism, and the three movable contacts on the sliding table conductively contact with different fixed contacts. Changeover time (each changeover time is averagely 10 minutes) of testers can be reduced, and all bushing tap ground insulation resistance tests of the transformer can be realized by wiring once.