The invention relates to a membrane air purifier. The membrane air purifier is cylindrical in the shape and composed of a control panel (1), an upper case (2), a middle case (3), a lower case (5) and a base (6). The control panel is arranged at the top of the air purifier. The upper case is provided with clean air outlets in the direction of 360 degrees. A round duct fan is arranged in the middle case. An air purification assembly is arranged in the lower case. The lower case is provided with air inlets in the direction of 360 degrees. The membrane air purifier can effectively filter PM2.5 in the air, can effectively prevent bacteria from breeding in the purifier to avoid the formation of secondary pollution, uses ultra-fine nano-photocatalysts material modified activated carbon as a VOC (Volatile Organic Compounds) purification component to effectively adsorb and decompose VOC under the action of a light source, is small in size and can achieve 360-degree air intake and clean air discharge so as to achieve multi-angle all-dimension air purification.