In order to explore the ripple formation mechanism in laser polishing, 718 Alloy and 304 stainless steel were polished by nanosecond fiber laser, and the ripple effect caused by laser polishing was investigated. Results show that there is a great difference between the ripple produced by laser polishing (the scale is tens of microns) and the laser pulse action distance (10 μm). Moreover, the ripple amplitude decreases with the decrease of laser energy, while the wavelength of the ripple changes little with the laser energy. According to the experimental results, the generation of ripple is a complex process involving the absorption of laser energy, melt flow, material evaporation and even pulse sequence. The source of ripple is the variation of melt flow caused by the laser ablation alternately to the melt and high temperature solid. The influence mechanism of laser energy on ripple is as follows: when a very high energy laser pulse is used, the input energy would be consumed by melt gasification, thus the increase of melt thickness as well as the ripple changes very little with energy. When the laser energy is in the range with less gasification, the decrease of laser energy would lead to the decrease of melt thickness as well as ripple amplitude.