Abstract: The influence of rolling parameters on trough fluctuation in natural circulation was researched. The mathematical model was developed to simulate trough fluctuation and the calculated results fit well with the experimental results. The calculated results indicate that for trough fluctuation under rolling motion, the additional force caused by rolling motion plays a main role in the whole flow fluctuation process, while near the trough, the local friction pressure drop and driving force caused by gravity dominate the flow alternately, which eventually induces instability near the trough. The bigger the amplitude and frequency of rolling motion are, namely the more intense the rolling motion is, the bigger the fluctuation of driving force caused by rolling is, thus causing larger fluctuation of flow rate and wall temperature, thereby the power corresponding to the starting point of trough instability is lower.