Abstract: Small break LOCA with auxiliary feedwater failure needs to implement feed and bleed cooling measures to prevent core damage. In this paper, the RELAP5 is used to establish the analysis model of HPR1000, and analyze the feed and bleed cooling of small break LOCA with auxiliary feedwater failure. A series of sensitivity analysis on some key factors influencing the success criteria of feed and bleed cooling is carried out, such as the number of safety valves of pressurizer, the failure time of auxiliary feedwater, the safety injection flow rate, etc. The analysis results show that: in order to alleviate the small break LOCA with auxiliary feedwater failure, the operator should open three pressurizer safety valves in time to implement the feed and bleed cooling. When the auxiliary feedwater fails delay 30 minutes after start-up, the operation time window will be greatly increased. SG water inventory, pressurizer safety valve flow and medium pressure safety injection flow have little influence on the operation time window. The analysis results can provide a reference for the study of the risk informed safety margin analysis method.