A　consensus　mechanism　for　blockchain　based　on　proof　of　contribution　(PoC)　is　a　kind　of　consensus　mechanism　that　is　suitable　for　the　application　scenarios　of　intellectual　property　protection　and　transaction.　In　the　PoC　mechanism,　the　contribution　values　of　user　nodes　are　calculated　periodically　and　the　node　with　the　largest　contribution　value　will　assume　the　right　for　the　construction　of　a　new　block.　However,　the　PoC　consensus　mechanism　has　the　problem　that　the　node　that　constructs　the　new　block　in　the　current　round　exhibits　the　property　of　strong　certainty.　If　the　node　that　is　supposed　to　construct　the　new　block　in　the　current　round　fails　to　do　so,　all　the　other　nodes　will　remain　in　the　waiting　state　and　the　system　will　hang　and　execution　can　no　longer　continue.　To　make　the　PoC　blockchain　consensus　mechanism　applicable　to　the　public　chain　scenario,　this　paper　proposes　a　new　consensus　mechanism　based　on　the　contribution　value　as　well　as　on　the　difficulty　value　in　the　proof　of　work　consensus　mechanism　(PoC+PoW).　In　the　PoC+PoW　consensus　mechanism,　some　uncertainty　is　added　into　the　process　of　determining　the　right　for　the　construction　of　a　new　block　to　overcome　the　shortcomings　of　the　original　PoC　consensus　mechanism.　In　PoC+PoW,　the　difficulty　values　of　the　mathematical　problem　that　participating　nodes　try　to　solve　in　the　PoW　competition　is　dynamically　determined　according　to　the　PoC　values　of　the　nodes.　The　proposed　mechanism　can　thus　be　viewed　as　a　disaster　recovery　scheme　for　the　PoC　consensus　mechanism　to　ensure　the　reliability　of　the　system　operation.　The　proposed　PoC+PoW　consensus　mechanism　would　allocate　a　corresponding　PoW　difficulty　value　to　a　node　according　to　the　ranking　of　the　contribution　value　of　the　node.　All　nodes　then　compete　for　the　right　for　bookkeeping　and　block　construction　through　the　PoW　consensus　mechanism.　The　new　consensus　mechanism　that　incorporates　PoW　would　still　fully　respect　the　ranking　of　the　contribution　values　from　PoC　to　ensure　that　the　probability　of　constructing　a　new　block　by　a　node　is　highly　proportional　to　its　ranking　among　all　the　contribution　values.　As　far　as　system　operation　is　concerned,　the　probability　of　block　construction　can　be　guaranteed　to　reach　or　approach　infinitely　to　100%,　which　should　effectively　solve　the　system　hanging　problem　existing　in　PoC-based　systems.　This　paper　will　present　the　design　of　an　algorithm　for　the　allocation　of　the　PoW　difficulty　values　from　three　aspects:　the　ranking　of　the　contribution　values,　the　difference　between　adjacent　contribution　values　and　the　grouping　method,　and　will　verify　the　rationality　and　effectiveness　of　the　proposed　allocation　algorithm　through　experiment.　In　addition,　a　comparison　between　the　new　PoC+PoW　consensus　mechanism　and　the　traditional　PoC　consensus　mechanism　in　terms　of　the　efficiency　of　block　construction　further　verifies　the　superiority　and　the　feasibility　of　the　proposed　PoC+PoW　consensus　mechanism.　©　2021,　Science　Press.　All　right　reserved.