In this paper, the flow instability and dynamic response characteristics of multi-loop natural circulation system under different local resistance and heating power are studied. Through numerical simulation, the influence of local drag coefficient on key parameters such as liquid flow rate, temperature and void fraction is analyzed, and the stability rule of the system under full power failure is revealed. The results show that the local resistance has a significant effect on the instability range and strength of the flow, and the stable operating range of the system presents a complex coupling relationship with the change of the resistance coefficient and power. Based on the experimental data, the operating characteristics of the system in power step are further discussed.