The “moth eye” micro-nano structure has recently attracted much attentions due to its high potential value in scientific, biomedical, and industrial applications. For example, by manufacturing specific micro-nanostructures on the surface of an optical device, the incident light would be reflected multiple times on its surface, which lets the surface achieve the co-called “light trap effect”, reducing the transmission loss caused by Fresnel reflection at the interface. Laser Induced Periodic Surface Structures (LIPSS) provide a robust, flexible, non-contact, simple, and low-cost potential method for the fabrication of large-scale surface micro-nanostructures. As the most frequently used material on optical devices, it is of great significance to study the fabrication of optical micro-nanostructures on fused silica surfaces.In this paper, by using Ti:sapphire femtosecond laser processing system, the general laws of femtosecond laser induced LIPSS morphology on fused silica samples have been studied. Through designed experiments, the effects of different laser fluence and repetition frequency, pulse number, spot size, and pulse spatial interval on the morphology of LIPSS on fused silica surface were studied. We also focus on how to obtain the high-quality LIPSS, which can have a great impact on the final performance of the device.Different fluences were first set in the experiments. It was found that at a laser fluence of 5 J/cm², irregularly arranged nanospikes were densely distributed in the crater, and at 7 J/cm², ripple-like structures appeared in the center of the crater. After that, as the laser fluence increased, the periodicity increased, accompanied by an increase in proportion. A laser surface plasma interference model is used to explain the relationship between periodicity and laser fluence, which is in good agreement with the observed phenomena.In order to investigate the effect of laser spot size (or the influence aera size of laser spot) on the morphology of LIPSS, diminished laser spot sizes were set to observe the changes. To further reduce the size of laser spot, the concept of threshold effect was adapted. The results show that by the reduction of laser spot size, the LIPSS stripe becomes more regular. A grating-like LIPSS with good quality can be obtained under the 1 μm diameter of laser spot when the laser fluence is set around 3.7 J/cm².The effects of pulse number and laser repetition rate on LIPSS were also studied in this work. The results showed that only some defects could be observed on the surface when the pulse number was set to 1. As the pulse number increased, the ripple-like structures gradually appeared, but were irregular. When the pulse number was set to be 10, relatively intact fringes showed up. It is found that the periodicity of the fringes showed a decreasing trend with the increase of the pulse number. It is also found that changing the laser repetition rate alone has no significant impact on the morphology of LIPSS.Considering that laser fabrication is a line scanning process, there is a certain spatial distance between pulses. Therefore, we studied the effect of pulse spatial interval on the morphology of LIPSS. The results showed that when the spatial interval of pulses is similar to the periodicity that the LIPSS structure under current parameter conditions, high-quality, regular, long-range arrayed grating structures can be obtained. Specifically, we adopt the following parameters, 1 μm diameter of laser spot, a scanning speed of 20 μm/s, repetition rate 100 Hz, and laser fluence 4.2 J/cm², and a highly regular long range aligned nanograting structure was fabricated, with a period of 200~300 nm and the depth of about 300 nm. The results found in this work may be conducive to promoting the development of surface micro-nano optical structures on fused silica.