Replica strong consistency is the basis of developing newly-developed P2P applications. This paper analyses current replica consistency maintenance algorithms, proposes a novel replica consistency maintenance algorithm - node heterogeneous degree-based consistency maintenance algorithm (NHDCOM) according to the characteristic of unstructured P2P system. NHDCOM denotes the replica node capability by node heterogeneous degree, NHD. It manages replica nodes using Chord protocol and collects their NHD along with a Replica Information-gathering Tree built through the finger table-based ring partition method. Moreover, a replica update problem model is abstracted in NHDCOM. And then a Minimum Delay Content Update Tree algorithm based on dynamic programming method is proposed to improve the update speed. Simulation results demonstrate that this method is more efficient in maintaining strong replica consistency for unstructured P2P systems.