A flat knitting machine structure with an adjustable gap between two knock-over bits, comprising: two needle beds (11, 12), disposed at interval respectively comprising a plurality of needles, wherein each of the plurality of needles defines a needle extending line and comprises a butt which is positioned on the needle extending line; and two cam systems, respectively disposed to face one of the needle beds (11 or 12), wherein each of the cam systems comprises a needle cam to provide the butts being placed and guide each of the plurality of needles to make a knitting stroke towards the gap, the two needle beds (11, 12) respectively comprise a plurality of knock-over bits disposed to correspond to each of the plurality of needles, the plurality of knock-over bits facing each other to define a gap, wherein a distance of the gap is equal to a space between two knock-over bits facing each other, wherein the flat knitting machine structure is characterized in that each of the plurality of knock-over bits comprises a control butt disposed at a same side as each of the butts, an extending section provided with the control butt, a bending section connected with the extending section and a loop hanging section connected with the bending section as well as paralleled to a front edge of one of the needles, and wherein each of the control butts is respectively positioned on one of the needle extending lines in which one of the plurality of needles is correspondingly disposed; and the two cam systems respectively comprise a knock-over bit cam providing the control butts being placed, wherein the knock-over bit cam is controlled to define a displacement stroke for driving the plurality of knock-over bits to change the size of the gap. two needle beds (11, 12), disposed at interval respectively comprising a plurality of needles, wherein each of the plurality of needles defines a needle extending line and comprises a butt which is positioned on the needle extending line; and two cam systems, respectively disposed to face one of the needle beds (11 or 12), wherein each of the cam systems comprises a needle cam to provide the butts being placed and guide each of the plurality of needles to make a knitting stroke towards the gap, the two needle beds (11, 12) respectively comprise a plurality of knock-over bits disposed to correspond to each of the plurality of needles, the plurality of knock-over bits facing each other to define a gap, wherein a distance of the gap is equal to a space between two knock-over bits facing each other, wherein the flat knitting machine structure is characterized in that each of the plurality of knock-over bits comprises a control butt disposed at a same side as each of the butts, an extending section provided with the control butt, a bending section connected with the extending section and a loop hanging section connected with the bending section as well as paralleled to a front edge of one of the needles, and wherein each of the control butts is respectively positioned on one of the needle extending lines in which one of the plurality of needles is correspondingly disposed; and the two cam systems respectively comprise a knock-over bit cam providing the control butts being placed, wherein the knock-over bit cam is controlled to define a displacement stroke for driving the plurality of knock-over bits to change the size of the gap.