Modeling is performed for focused‐ion‐beam (FIB) sputtering and redeposition on trench sidewalls in a steady state approximation. Calculations are carried out to demonstrate the sputtered surface profile under known parameters such as sputtering yield as a function of ion incident angle, the FIB current density profile, and the FIB scan speed. It is found that a steplike slope with a gradient angle of θ0is formed at the FIB bombarding position. Furthermore, the redeposition flux on the sidewalls is calculated as a function of θ0for the FIB trench milling assuming the cosine law for the angular distribution of the sputtered atom. The redeposition will be more accurately predictable and controllable when more information about these assumptions is obtained.