Laser-induced damage threshold (LIDT) is a key parameter for optical components heavily influenced by the surface roughness in high-power laser uses. Present polishing technologies often bring about directional micro waviness to the optical surfaces due to path effect. Roughness features of a K9 glass surface were studied in this paper. A new evaluating restriction for power spectral density specification was established, and the off-specification frequency contents were found out. Then the electromagnetic simulation of light field modulation was carried out, and the field enhancement factor reached 12.04, verifying the impact of these contents on the laser damage performance of optical components. To restrain the modulation effect by the textures, electrorheological finishing (ERF) technology was proposed, and the processing was undertaken on the K9 surface. Roughness data converged to minimal Ra 1.00 nm, and the angular spectrum decreased in expected ranges. ERF proved to be effective in eliminating the directional textures and restraining the light intensity modulation of the textures. As a result, the LIDTs of optical components can be improved by ERF processing.