A garment simulation method and device according to an embodiment: receive a user input selecting, from a simulated three-dimensional garment worn by an avatar, one of a plurality of objects corresponding to the next depth level after the depth level currently being displayed among depth levels for hierarchically displaying one or more pieces included in the three-dimensional garment and two-dimensional patterns constituting the respective pieces; display the next depth level by controlling the visualization of the plurality of objects so that the selected objects are not hidden by one or more of the remaining objects other than the selected objects among the plurality of objects; modify the selected objects corresponding to the next depth level on the basis of inputs for editing the selected objects; modify the three-dimensional garment to reflect the modifications to the selected objects; and output the modified three-dimensional garment.