The invention discloses a 
system and a method for constant 
water level sequential batch type 
sewage treatment system with 
continuous variable volume. The method includes continuously injecting 
sewage into a constant 
water level variable volume adjusting area to enable an adjustable 
volume area to float on the liquid level in separation mode, injecting water to a constant 
water level variable volume reaction area through a distribution pump, injecting water to a constant water level variable volume 
water quality stabilizing area through a constant water level water 
decanting device and a waterdecanting pump, enabling supernate after reaction to be discharged into the supernate of the a constant water level variable volume 
water quality stabilizing area on the other side of the constant water level variable volume reaction area, pass through a 
smoothing clearing area and finally pass through an inclined plate clearing area and continuously discharging purification 
water equivalent withpreprocessing feeding water. The 
system and the method resolve the technical problem that 
denitrification and dephosphorization efficiency is low, 
single process structure water outlet index cannot meet requirements of indexes of the 
national standard first grade A, and process structure is complex. The 
system has the advantages of being simple in structure, low in integral process 
energy consumption, good in 
processing effect and the like.