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In a 5G millimeter wave system, beam misalignment between a gNB and an UE may occur due to sudden fluctuations in the channel, user rotation, and so on. The beam failure recovery mechanism can help the gNB or the UE change its current failed beam to alternative(feasible) beam(s) based on beam measurement, thereby avoiding the frequent radio link failure caused by beam misalignment. This paper systematically expounds the design and implementation of beam failure recovery in 5G, including beam failure detection, candidate beam identification, beam recovery request transmission and gNB response，to provide essential reference for further research on beam failure recovery.