A stapling head assembly comprising: a cartridge support, equipped detachably with a cartridge; a connecting tube, wherein a distal end thereof connects to a proximal end of said cartridge support, there is a first limiting groove set at a side wall of said connecting tube along a longitudinal direction thereof,; a cutter pushing rod, set movably inside said connecting tube and comprising a first blocking portion set at a proximal end of the cutter pushing rod; and a lockout mechanism, connecting to said connecting tube, characterized in that, said lockout mechanism comprises: a pressing block comprising a second blocking portion and a second guiding portion protruding from a side wall of one side of a distal end of the pressing block, said pressing block connects to an inside of said first limiting groove by a pin, an axis of the pin is traverse to the longitudinal direction of the connecting tube; and a pushing block comprising a radially outward oriented surface forming a first guiding portion, wherein, the first guiding portion orients to a distal end of said pushing block, and inclines upwards from a distal end to a proximal end thereof, said pushing block is located at one side of said pressing block; wherein, when said pressing block is located at a first position, said second blocking portion clamps with said first blocking portion, to prevent said cutter pushing rod from moving; when said pushing block moves from a third position to a fourth position relative to the connecting tube along the longitudinal direction of the connecting tube, said first guiding portion pushes said second guiding portion, so said pressing block rotates around the pin relative to the connecting tube to move from said first position to a second position, such that said second blocking portion departs from said first blocking portion, and said cutter pushing rod is movable along the longitudinal direction of the connecting tube. a cartridge support, equipped detachably with a cartridge; a connecting tube, wherein a distal end thereof connects to a proximal end of said cartridge support, there is a first limiting groove set at a side wall of said connecting tube along a longitudinal direction thereof,; a cutter pushing rod, set movably inside said connecting tube and comprising a first blocking portion set at a proximal end of the cutter pushing rod; and a lockout mechanism, connecting to said connecting tube, characterized in that, said lockout mechanism comprises: a pressing block comprising a second blocking portion and a second guiding portion protruding from a side wall of one side of a distal end of the pressing block, said pressing block connects to an inside of said first limiting groove by a pin, an axis of the pin is traverse to the longitudinal direction of the connecting tube; and a pushing block comprising a radially outward oriented surface forming a first guiding portion, wherein, the first guiding portion orients to a distal end of said pushing block, and inclines upwards from a distal end to a proximal end thereof, said pushing block is located at one side of said pressing block; wherein, when said pressing block is located at a first position, said second blocking portion clamps with said first blocking portion, to prevent said cutter pushing rod from moving; when said pushing block moves from a third position to a fourth position relative to the connecting tube along the longitudinal direction of the connecting tube, said first guiding portion pushes said second guiding portion, so said pressing block rotates around the pin relative to the connecting tube to move from said first position to a second position, such that said second blocking portion departs from said first blocking portion, and said cutter pushing rod is movable along the longitudinal direction of the connecting tube. a pressing block comprising a second blocking portion and a second guiding portion protruding from a side wall of one side of a distal end of the pressing block, said pressing block connects to an inside of said first limiting groove by a pin, an axis of the pin is traverse to the longitudinal direction of the connecting tube; and a pushing block comprising a radially outward oriented surface forming a first guiding portion, wherein, the first guiding portion orients to a distal end of said pushing block, and inclines upwards from a distal end to a proximal end thereof, said pushing block is located at one side of said pressing block; wherein, when said pressing block is located at a first position, said second blocking portion clamps with said first blocking portion, to prevent said cutter pushing rod from moving; when said pushing block moves from a third position to a fourth position relative to the connecting tube along the longitudinal direction of the connecting tube, said first guiding portion pushes said second guiding portion, so said pressing block rotates around the pin relative to the connecting tube to move from said first position to a second position, such that said second blocking portion departs from said first blocking portion, and said cutter pushing rod is movable along the longitudinal direction of the connecting tube.