The mixed reality based 3D sketching device includes a processor; and a memory connected to the processor. The memory stores program commands that are executable by the processor to periodically tracks a marker pen photographed through a camera, to determine whether to remove a third point using a distance between a first point corresponding to a reference point, among points that are sequentially tracked, and a second point at a current time, a preset constant, and an angle between the first point, the second point, and the previously identified third point, to search an object model corresponding to a 3D sketch that has been corrected, after correction is completed depending on the removal of the third point, and to display the searched object model on a screen.