The utility model provides an on -load tap -changer based on vacuum tube, the on -load tap -changer body that includes the low pressure serial -to -parallel conversion that the high pressure transform that has three -phase high pressure inlet wire end and three -phase low -voltage wire inlet held, be provided with the vacuum tube between the three -phase high pressure inlet wire end of the on -load tap -changer body of the high pressure transform of three -phase high pressure inlet wire end and be provided with the vacuum tube between each coil of taking a fancy to at the low pressure serial -to -parallel conversion's of three -phase low -voltage wire inlet end on -load tap -changer body, change the three -phase end of high pressure transform respectively through the vacuum tube, change the coil of each looks of low pressure serial -to -parallel conversion respectively through the vacuum tube, no longer transfer and hold directly switching of switch adoption, no longer contact burning, consequently, on -load tap -changer's safety margin has been improved.