Electroencephalogram(EEG) contains a large amount of brain function state information, and has been widely applied in many fields, such as cranial nerve disease diagnosis, brain-computer interface, and sleep stage and anesthetic depth monitoring. EEG is a weak bio-electric signal, whose amplitude is just microvolt and frequency is lower than 150 Hz. Since EEG is easily interfered by signals, like electro-oculogram and electrocardiogram, effective extraction of EEG is key to EEG analysis. An EEG acquisition system based on STM32 was designed to realize effective acquisition of EEG. In this system, EEG signals were sensed by three lead biological electrodes on the forehead, then amplified through multistage amplification in the front analog circuit and filtered by passive filter or active filters. Meanwhile, electrical level rising circuit and electrode connection state detection circuit were also added in. After that, EEG signals were converted to digital value by 12 bit analog-to-digital converter, and then transferred to upper computer via bluetooth module to realize effective extraction and transmission, providing the basis for further processing and analysis. The effectiveness of this EEG acquisition system was verified by comparing output with other similar products.