The increasing application and deployment of blockchain in various services necessitates the assurance of the effectiveness of PBFT (Practical Byzantine Fault Tolerance) consensus service. However, the performance of PBFT consensus service is challenged in dynamic scenarios. The paper explores how to reduce the consensus processing time and maintenance cost of PBFT consensus service under software aging in dynamic scenarios. We first propose a PBFT system, consisting of three subsystems, one active-node subsystem, one standby-node subsystem and a repair subsystem. All the active nodes participate in the consensus and all standby nodes aim for fault-tolerance. Each aging/crashed nodes become standby nodes after completing its repairing in the repair subsystem. The nodes migrate between the active-node and standby-node subsystems in order to support the continuity of the PBFT consensus service while reducing maintenance cost. Then, we develop a Markov-chain-based analytical model for capturing the behaviors of the system and also derive the formulas for calculating the metrics, including consensus processing time, PBFT service availability, the mean number of nodes in each subsystem. Finally, we design a Multi-Objective Evolutionary Algorithm-based method for minimizing both the PBFT service response time and the PBFT system maintenance cost. We also conduct experiments for evaluation.