The invention discloses a water inlet device and a water inlet method for an 
anaerobic reactor. Most of 
anaerobic bacteria are strictly 
anaerobic bacteria which are extremely sensitive to 
oxygen; and however, in practice, inlet water is required to be changed every day or 
every other day, so that controlling dissolved 
oxygen in the inlet water of the reactor to a relatively low level becomes very important. The water inlet device consists of three parts, namely a water inlet 
barrel, a water inlet 
barrel cover and a gas producing main body, wherein a feed port is formed in the water inlet 
barrel cover; the water inlet barrel cover is connected with the gas producing main body through a connecting component; the gas producing main body is fixed through the connecting component and a 
siphon; a 
solid material is fed from the feed port, a liquid material is fed through the 
siphon, and after gas-liquid mixing, a gas producing reaction can be performed; and the 
solid material is 
carbonate or 
bicarbonate, the liquid material is acid, and produced gas is CO2 which forms a CO2 
atmosphere. Through the water inlet device and the water inlet method, continuous 
dissolution of 
oxygen in air into the inlet water can be simply and effectively prevented, so that the low-oxygen state of the inlet water is kept; besides, the produced CO2 can supplement an inorganic 
carbon source required by autotrophic 
bacteria, so that the growth of anaerobic autotrophic 
bacteria and stable operation of the 
anaerobic reactor are facilitated.