The invention relates to a method and device for realizing the lasting and stable accumulation of 
nitrite nitrogen under a low-temperature condition. The lasting and stable accumulation of the 
nitrite nitrogen is completed in two stages of biological aerated filter systems. The method comprises the following steps: step a. starting a first-stage biological aerated filter and a secondary-stage biological aerated filter, cleaning a 
filter material, soaking, forming a 
biofilm, commissioning and operating; b. preparing testing 
wastewater, and maintaining 
water temperature at 6 to 10 DEG C; c. enabling 
wastewater to flow out from a head tank and enter the first-stage biological aerated filter from below; and d. enabling yielding water of the first-stage biological aerated filter to enter the secondary-stage biological aerated filter from bottom to top in the same way. The 
nitration types of the two stages of biological aerated filter are 
nitrous acid-type 
nitration, the stable accumulation of NO2--N in the yielding water is shown, the accumulation rate is 63.2% to 79.8%, and the accumulation time is up to 30 to 35 days. The method has the advantages that the 
biofilm process adopting the two stages of biological aerated filters can be used for solving the problems of 
high energy consumption at a high temperature (30 to 40 DEG C), and 
sludge bulking under a low DO (Dissolved 
Oxygen) condition, and the effective removal of organic matters in 
wastewater with a low C / N ratio (less than 3) and the lasting and stable accumulation of NO2--N are realized.