Abstract: Experimental studies on the natural circulation steady-state characteristics of an integrated small reactor were carried out on the full-scale simulation platform in the Institute of Nuclear and New Energy Technology of Tsinghua University. The results show that the natural circulation flow in the primary loop maintains symmetry, when the outside conditions are set to be identical. The main factor affecting the natural circulation flow rate is the heating power, while the inlet temperature and system pressure have a relatively small impact on it. An integrated feature parameter k representing the natural circulation ability of systems was proposed and derived, which can be used to evaluate the natural circulation ability of different natural circulation loops.