The invention provides an online flexible decoking device for an ascending pipe and a decoking and heat transfer enhancement method thereof. The online flexible decoking device comprises an external driving device 1, a top-hanging fixed bracket, a driven bracket 3, a hanging chain or rope 4, an impeller blade 5 and a sealing device 6. Through rotation of the hanging chain or rope, real-time cleaning of coked particles is realized to achieve the purposes of flexible decoking, heat resistance reduction and heat transfer enhancement; while decoking, the air flow of raw coke oven gas can be disturbed through an impeller, the heat transfer power is improved and the heat transfer enhancement is realized.