ObjectiveTo research the relevancy between the amplitudes of EMG signal of recurrent laryngeal nerve (RLN) during thyroidectemy with the movement of vocal cords after operation by applying the intraoperative neuromonitoring (IONM) and verify the proper warning criterion. MethodsFrom April 2013 to October 2013, 130 patients (214 nerves at risk) underwent complex thyroidectomy with the application of IONM. According to the degree of amplitude changing on different sites of RLN (proximal site and distal site) before closing incision, all the patients were divided into 10 groups. Every patient's vocal cords movement after operation by laryngoscopy and simulated the neural function in real time were compared. ResultsSeven patients got abnormal movement of vocal cords, the corresponding amplitudes of the EMG signal of RLN were in the range between 0 to 50%, 1 case from Group 6 (40%≤Rp/Rd<50%), 1 case from Group 8 (20%≤Rp/Rd<30%), 1 case from Group 9 (10%≤Rp/Rd<20%), 4 cases from Group 10 (0≤Rp/Rd<10%), and there's no permanent RLN palsy. ConclusionThe final amplitude of RLN decrease below 50%R1 would probably lead to vocal cords' abnormal movement, and when it decrease below 30%R1, the possibility of abnormal movement would increase; 50% decrease of EMG amplitude can be used as a warning criterion to prevent nerve function damage.