NOVELTY - Low carbon-nitrogen (C/N) ratio domestic sewage Haliscomenobacter hydrossis filamentous bacteria microexpansion is carried out by preparing a sludge microexpansion system having an anoxic area (23) and aerobic area (24) and including cellular nitrification liquid pipeline; reflowing sludge to anoxic area and circulating nitrification liquid from aerobic area to anoxic area; and after 13 days of operation, generating microexpanded Haliscomenobacter hydrossis filamentous bacteria.    USE - Method for low carbon-nitrogen (C/N) ratio domestic sewage Haliscomenobacter hydrossis filamentous bacteria microexpansion (claimed).    ADVANTAGE - The method can fast start expansion of H. hydrossis, has enhanced synchronous nitrification and denitrification effect of system and increased pollutant removing effect, and is capable of saving aeration energy consumption.    DETAILED DESCRIPTION - Low C/N ratio domestic sewage Haliscomenobacter hydrossis filamentous bacteria microexpansion comprises: (A) preparing a sludge microexpansion system having an anoxic area (23) and including a stirring device, an aeration device, a water tank (1) connected to water inlet pipe and anoxic area, an aerobic area (24) connected to anoxic area, an overall reactor (9), a secondary sedimentation tank (12), a cellular nitrification liquid pipeline (21), and a control switch (3); (B) maintaining mixed liquor suspended solid (MLSS) concentration in aeration pool at 2000-3500 mg/L, maintaining constant temperature of 20-30 degrees C, regulating pH value to 7-8 and controlling C/N ratio to 2-5 and organic load at 0.22-0.30 kg chemical oxygen demand (COD)/kg MLSS, then precipitating sludge, reflowing to anoxic area, circulating nitrification liquid from aerobic area to anoxic area, and removing COD to less than 20% content; and (C) adjusting gas flow so that dissolved oxygen in aerobic area has average count of 0.3-0.8 mg/L, and after 13 days of operation, generating microexpanded Haliscomenobacter hydrossis filamentous bacteria.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of a system for domestic sewage Haliscomenobacter hydrossis filamentous bacteria microexpansion.    Water tank (1)    Control switch (3)    Overall reactor (9)    Secondary sedimentation tank (12)    Cellular nitrification liquid pipeline (21)    Anoxic area (23)    Aerobic area (24)