An online repairing device for seal surface of high pressure pipeline is a maintenance device for pressure vessel and high pressure pipeline, which overcomes the shortage of original technology. It is connected by a tension clamping chuck, a reamer, a main spindle cutter head, a reamer locking bolt, a feed handwheel, a tension handwheel, inlet pipe and high pressure flange. The tension clamping chuck is installed on the high pressure flange; the reamer is fixed on the main spindle cutter head; the feed handwheel and the tension handwheel are installed at one end of the tension clamping chuck; the inlet pipe is located inside the main spindle cutter head. The design effects are as follows: the cutting performance is fine; the grinding accuracy is high; the most outstanding point is that the work efficiency is 8 -10 times higher compared with the routine repairing method and it greatly relieves the labor intensity of workers; the device is simply, is with little investment, large agility and fast effect, which is more applicable for the quick site repairing for the seal surface such as online pipeline, flange, etc of small chemical industrial enterprises and modernized chemical industrial enterprises without mechanical process ability.