Abstract: Visual experiments on bubble density were carried out at subcooled flow boiling in a narrow channel under rolling and inclination conditions. Image analysis based results show that the bubble density fluctuates periodically under rolling condition. It is found by data comparison that the bubble density fluctuation amplitude increases with the decrease of rolling period, while the fluctuation form doesn’t vary considerably. The increase of rolling angle for a given rolling period reduces the bubble density, but results in an almost invariable fluctuation form. In regard to inclination conditions, when the heating plate of the test section lies at lower side (positive angle inclination), the bubble density decreases with the increase of inclination angle. When the heating plate is at upper side (negative angle inclination), the bubble density first decreases then increases with the increase of inclination angle. Comparison of bubble densities shows that the bubble density at the maximum angle during rolling is close to that under the corresponding inclination.