Abstract: The natural circulation capacity and related characteristics of passive residual heat removal system under rolling motion were investigated experimentally on the rolling apparatus. The effect of additional and gravity pressure drop on flowing characteristic was studied. And the influence of gravity pressure drop and flow resistance upon flow velocity was also analyzed. It is shown that the natural circulation capacity of passive residual heat removal system reduces in rolling motion. As the rolling amplitude becomes larger, the average condensate flow rate becomes smaller, and its oscillation amplitude becomes larger. Moreover, the minimum condensate flow rate decreases quickly. But the change of maximum condensate flow rate is limited. The variation of main parameters with rolling period is not very obvious. The effect of additional pressure drop on average flow velocity is not noticeable. The influence of gravity pressure drop on average flow velocity has nothing to do with rolling period. The effect of gravity pressure drop on flow velocity is much more less than that of flow resistance. As the rolling amplitude becomes larger, the effect of flow resistance on average flow velocity diminishes.