Redeposition is a common phenomenon in focused ion beam （FIB） sputtering， rendering the absence of a steep sidewall and actual processing size to be considerably different from the proposed design， particularly for high-aspect-ratio microstructures. To improve FIB microsputtering， a single-pixel line-assisted sputtering （SLAS） protocol based on local correction by additional sputtering is proposed to eliminate the redeposition effect and to significantly improve the perpendicularity of V-type sidewalls for a trench microstructure. A theoretical method based on a continuous cellular automaton （CCA） was utilized to simulate the redeposition effect and the perpendicularity improvement of V-type sidewalls upon the application of SLAS. Moreover， the CCA-based simulation suggested a contradiction between sidewall improvement and broadening of the ion beam spot. Further experiments demonstrated the validity of SLAS and confirmed the precise position of the SLAS area for achieving the best elimination of redepositing residue. Microtrenches of 100 nm in width were fabricated with satisfying steep sidewalls and a 3∶1 aspectratio. Generalizing this in situ elimination of redeposition in the field of FIB sputtering would be effective.