In MMCHVDC system, the AC transient faults will bring overcurrent and overvoltage occurred on arms of rectification and inverter station, as well as abnormal operating state. To evaluate the operating state of MMCHVDC system is a new issue by using electrical information of MMC when AC transient faults or disturbance occur. To address this issue, this work firstly analyzes the influence of AC transient faults on the electrical signals in MMC in detail, and investigates the relationship of electrical information in MMC. Then, considering system damping, irregular change and complex frequency of the currents and voltages and disturbance feature with low energy in MMC, Renyi wavelet packet energy entropy (RWPEE) is utilized to extract feature of AC transient faults. Based on the feature extraction, the evaluation index set is obtained. In combination of Renyi entropy weight and grey relational analysis, a novel evaluation method is proposed to evaluate operating state of MMCHVDC system when AC transient faults occur. Finally, 2terminal 31level MMCHVDC is used to generate experimental data, and operating state of MMCHVDC system is evaluated. The experimental results prove the effectiveness of the proposed method.