A sheet medium separating mechanism and a control method and a control system thereof. When the head part of a currently separated medium reaches the front boundary of a preset speed regulating region in front of a money distributing wheel (111) and the tail part of the currently separated medium leaves the back boundary of a preset speed regulating region on the money distributing wheel, relative speeds of a money distributing wheel motor (122) and a back money distributing power wheel motor (120) are regulated, so that a preset medium separating distance is kept between the tail part of the currently separated medium and the head part of a next separated medium. Therefore, the sheet medium separating mechanism is adapted to sheet media of different shapes and different specifications, the money distributing wheel size and rotary inertia of longitudinal deposit equipment are reduced, and the motor load is effectively lowered.