The load distribution and coupling feedback between parallel loops is one of the issues in the multi-loop nuclear reactor system. In the present study, a dual-loop reactor natural circulation experimental system with typical structural features was designed and built based on the characteristics of a floating nuclear power plant. The system is used to study the system response characteristics under the conditions of heat load disturbance, resistance disturbance and system response time. The results show that the flow of the primary loop will be redistributed when the load disturbance was introduced into the natural circulation loop. The primary flow rate changes quickly when the heat load disturbance reaches the critical point. When the heat load disturbance is lost on one side, the total natural circulation flow rate of the loop decreases to 60% of the value in the steady-state flow. The response of the system after introduction of resistance disturbance is similar to the introduction of the load disturbance. The response of the system can be divided into two stages, i.e., the rapid response period and the slow adjustment period after the introduction of the disturbance. With the increase of disturbance, the negative slope of stage 1 increases, and the slope of stage 2 gradually changes from positive to negative. With the experimental, a model is developed to predict the response of the system. A characteristic number S is defined to characterize the symmetry of the system. Based on the experimental data, it is found that when S is between 0.5–2, the external disturbance will not cause asymmetric response of the system.