A control method for positioning is provided, which is applicable to a radiotherapy system. The method includes: acquiring a plurality of first body surface coordinates of a target site in a three-dimensional body surface image of a treatment object on a treatment couch; acquiring a plurality of second body surface coordinates under an isocentric coordinate system by transforming the first body surface coordinates using a target transformation matrix corresponding to the first placement position; determining, based on the plurality of second body surface coordinates and a contour image of the target site in the treatment plan, a placement offset of the target site, so as to control the treatment couch to move until the placement offset of the target site upon the movement meets a target offset requirement.