Abstract: In the view of the characteristics of the single-phase natural circulation flow under rolling motion, the research was conducted experimentally. The result showed that the fluid fluctuated under rolling motion, and the frequency of the fluctuation was the same as the rolling frequency. The theoretical analysis showed that the rolling influenced the natural circulation in two aspects, i.e., on one hand rolling motion changed the system position and then changed the natural circulation thermal driven head; on the other hand the additional acceleration by the rolling imposed an additional pressure drop on the fluid. A model of the ingle phase natural circulation flow under rolling condition was constructed. The effects of rolling perid, rolling amplitude and other parameters upon the natural circulation were analyzed and the influence rules were obtained.