A flat knitting machine stitch presser device, comprising: a fixing base disposed on a cam supporting base; characterized in that the position of the stitch presser device varies with gap size and in that it comprises a driving element started when a knock-over bit cam makes a displacement stroke; a sliding base disposed correspondingly to the fixing base and provided with a guide block, the sliding base making a regulation stroke relative to the cam supporting base when the driving element is started; a limiting block combined with the fixing base and limiting the sliding base to only slide relative to the cam supporting base; a stitch presser sheet supporting arm fixed to a yarn feeder guide rod with one end of the stitch presser sheet supporting arm and provided with an installing base on the other end of the stitch presser sheet supporting arm, wherein a passage is formed in the installing base; and a stitch presser sheet comprising a control section connected with the guide block, a connection section extending from the control section and penetrating through the passage, and a stitch presser section extending from the connection section and facing a needle bed, wherein the control section leads the stitch presser section to move when the sliding base makes the regulation stroke, so as to change a stitch presser position. a fixing base disposed on a cam supporting base; characterized in that the position of the stitch presser device varies with gap size and in that it comprises a driving element started when a knock-over bit cam makes a displacement stroke; a sliding base disposed correspondingly to the fixing base and provided with a guide block, the sliding base making a regulation stroke relative to the cam supporting base when the driving element is started; a limiting block combined with the fixing base and limiting the sliding base to only slide relative to the cam supporting base; a stitch presser sheet supporting arm fixed to a yarn feeder guide rod with one end of the stitch presser sheet supporting arm and provided with an installing base on the other end of the stitch presser sheet supporting arm, wherein a passage is formed in the installing base; and a stitch presser sheet comprising a control section connected with the guide block, a connection section extending from the control section and penetrating through the passage, and a stitch presser section extending from the connection section and facing a needle bed, wherein the control section leads the stitch presser section to move when the sliding base makes the regulation stroke, so as to change a stitch presser position. a driving element started when a knock-over bit cam makes a displacement stroke; a sliding base disposed correspondingly to the fixing base and provided with a guide block, the sliding base making a regulation stroke relative to the cam supporting base when the driving element is started; a limiting block combined with the fixing base and limiting the sliding base to only slide relative to the cam supporting base; a stitch presser sheet supporting arm fixed to a yarn feeder guide rod with one end of the stitch presser sheet supporting arm and provided with an installing base on the other end of the stitch presser sheet supporting arm, wherein a passage is formed in the installing base; and a stitch presser sheet comprising a control section connected with the guide block, a connection section extending from the control section and penetrating through the passage, and a stitch presser section extending from the connection section and facing a needle bed, wherein the control section leads the stitch presser section to move when the sliding base makes the regulation stroke, so as to change a stitch presser position.