Abstract: Integrated pressurized water reactor (IPWR) owns more than one once through steam generators (OTSGs). Flow instability may occur in secondary side of OTSG under certain conditions. Trying to avoid the occurrence of flow instability is of great importance for the safe and stable operation of OTSG. Because of the fact that flow instability often occurs in certain regions, so when OTSGs operate with low load, OTSGs can be divided into several groups, which can avoid flow instability. Operational characteristics of IPWR were analyzed by RELAP5/MOD3.4 code and during the discussion of group operation, a rapid change load operation scheme using OTSG group operation mode which could be used in IPWR was analyzed. The results show that OTSG group operation mode can effectively avoid flow instability, which can ensure IPWR operate stably under low load condition.