The invention discloses an insulation caliper unit and aims at providing an insulation caliper unit that is capable of surveying the type and specification of a conductor accurately while the normal working of the conductive line are not affected. The insulation caliper unit comprises an insulation rod, a vernier caliper, and an after-measurement vernier locking device. The vernier caliper consists of a main ruler, a vernier sliding base arranged on the main ruler in a sliding mode, and an outer diameter measuring structure; the main ruler is connected with one end of the insulation rod; and the outer diameter measuring structure includes a fixed external measuring claw arranged on the main ruler, and a moving external measuring claw arranged on the vernier sliding base. The after-measurement vernier locking device consists of a guide rail arranged on the vernier sliding base, a sliding block sliding along a guide rail, a trigger push rod arranged on the sliding block, a locking bolt being arranged on the vernier sliding base and being used for locking the vernier sliding base at the main ruler, a driving gear arranged at the locking bolt, and a tooth bar being arrange at the tripper push rod and being engaged with the drive gear.