Abstract: If the AC system fault causing the first commutation failure is not cleared or improper control is adopted during the fault recovery stage, the subsequent commutation failure may occur in the recovery process of the DC system. Based on the commutation voltage-time area, this paper analyzes the direct and indirect influencing factors leading to the subsequent commutation failure, and clarifies the mechanism of subsequent commutation failure. In order to quantitatively evaluate the risk of subsequent commutation failure, the subsequent commutation failure risk index（SCFRI） is proposed, and an additional control strategy based on SCFRI is proposed to adaptively adjust the triggering angle according to the risk degree. In order to avoid the limitation of additional control range, a coordinated current limiting strategy based on SCFRI is proposed. The two strategies cooperate with each other to effectively suppress the subsequent commutation failure. Taking the CIGRE DC transmission standard model as a testing example, the effectiveness of the proposed SCFRI and suppression strategies is verified.