Abstract: A high-performance EEG signal amplifier was designed, where the differential amplifier circuit, driven-right-leg circuit and preamplifying parts in the designed amplifier can denoise the common-mode interference signals. With the EEG signal amplified by the preamplifier and 2-stage post-amplifier, two low-pass filters and two 50Hz traps were arranged reasonably in design to denoise the high/medium-frequency interference in EEG signal effectively, thus enabling the efficient EEG signal detection without shielded enclosure. Testing results showed that the performance of all parts of the amplifier comes up to the indices as required in design. The effectiveness of the design was proved by the real EEG signal sampled from the scalp of the detected person.