Control method for automatic focusing and device thereof

The embodiment of the invention discloses a control method for automatic focusing and a device thereof. The method includes the steps of updating a focusing evaluation value for the current position of a focusing lens, acquiring the focusing evaluation values of a previous corresponding point and a next corresponding point for the current position of the focusing lens according to stored positioncodes of the corresponding points of the focusing evaluation values and the position of the focusing lens, acquiring changing trends of the current position of the focusing lens and the focusing evaluation values of the previous and next corresponding points, and finally determining the step length that the focusing lens moves according to the changing trends. In the embodiment of the invention, the moving step length of the focusing lens is determined according to the changing trends of the current position of the focusing lens and according to the focusing evaluation values of the previous and next corresponding points, so that only fine adjusting is carried out on the focusing lens in peak zones; therefore, the step length is small when the top point is found, the position of the focusing lens is changed little, the changing rate of the focusing evaluation values is low, and images cannot easily generate deceptive movement.