The objective of this study is to design a meal assistance system operated by electromyogram (EMG) signals. The system consists of four parts, EMG data acquisition, onset analysis, control circuit and operation of meal assistance robot. An algorithm based on EMG power with adaptive threshold is proposed for onset analysis, and applied to the operation of robot via control circuit. The performance of EMG-control system is tested in rate of success and comfort by both subjective and objective indices. The results show EMG signals acquired from active muscles in a human body can be used as control signals for the apparatus, by the proposed onset detection algorithm with adaptive threshold. The high rate of success and comfort of meal assistance system operated by EMG signals guarantee its use for patients with disabled upper limbs.