The invention provides a gravity-flow 
membrane bioreactor with low 
energy consumption. The gravity-flow 
membrane bioreactor comprises a reactor tank, a guide cylinder, an aerator, a MBR membrane 
assembly, an inflow water 
distribution system, a MBR fan, a process fan, a vacuum suction 
system, a constant-flow automatic regulation 
system and an internal 
sludge circulation 
system. According to the invention, a MBR membrane is arranged on the top of the 
bioreactor and 
siphon is realized through full use of liquid level difference, so power-
free water production is realized; since the MBR membrane 
assembly is located on the upper part of a biochemical 
aeration system, air for biochemical 
aeration can be fully used again for scrubbing of the membrane, so considerable air needed in scrubbing of the membrane is saved; and an anoxic area is formed in the bottom of a 
reaction zone, so a high-efficiency A / O 
denitrification function is obtained. The gravity-flow 
membrane bioreactor provided by the invention is a high-efficiency biochemical system realizes organic combination of power-
free water production, reduction in air demand, 
high oxygen transfer efficiency, integrated anoxic / aerobic treatment, 
sludge backflow without extra power, production of high-quality water and the like.