The Laser-induced Damage Thresholds (LIDTs) of fused silica optical elements would be deteriorate, when it suffers the 355 nm laser irradiation. This paper proposes a method to improve their LIDTs. A silica element was immersed into two types of HF-based etchants: 1.7%wt. HF acid and buffer oxide etchant (BOE: the mixture of 0.4%wt. HF and 12%wt. NH4F)to be treated in the same experimental condition , respectively. The etching rate was calculated by measuring the weight variation of the etching element during the etching process, and the surface roughness of the element was tested by a Zygo contourgraph. Then, the LIDT characteristics of the fused quartz element under the 355 nm laser irradiation were studied. The damage testing shows that the LIDT is relative to the depth of material removal. Both the etchants increase the LIDT at a certain depth of material removal, but further removal of material lowers the LIDT markedly. The etching rates of both etchants keep steady in our processing procedure, they are ~85.9 nm/min and ~58.6 nm/min, respectively. The micro-surface roughness (RMS&PV) increases as etching time extended. Furthermore, the hardness and Young's modulus of the fused silica etched were measured by a nano-indenter, and there is no solid evidence that LIDT can be related to hardness or Young's modulus.