Abstract: Based on a multiple cooling loops integrated reactor, we derived the theoretical solution of the natural circulation flow of multi-loop circuit. The perturbation coefficient m are obtained by using approximation and fitting approach, and the perturbation characteristics of the natural circulation system is analyzed and verified on an integrated reactor. The results indicate that for a symmetrical loop consisted of multiple cooling loops, the change of the flow is a function of Reynolds number Re and the ratio of the rising resistance characteristics and the falling resistance characteristics R_r. The perturbation coefficient m has a close relation with Re and R_r, and increases when R_r decreases. The greater the m, the smaller the effect of the same perturbation on the natural circulation system, that is to say, m can represent the anti-perturbation ability of the system.