The invention relates to the technical field of medical instruments, in particular to a special hand guard closing and clamping mechanism for an arterial blood gas needle. The mechanism consists of main clamping cylinders, fixed grooves, connecting wires, fastening cylinders, inserting strips, non-return rings, a needle tip groove, needle tip clamps, a protective plate, a needle stem groove, transition grooves, a pintle groove, a buckle and a connecting sheet. Each main clamping cylinder is of a columnar structure with a semicircular cross section, the needle tip clamps are of a semi-circular-truncated-cone-shaped structure, the vertical flat wall of the needle tip clamp is provided with the vertical needle tip groove, and the middles of the two main clamping cylinders are located in semi-cylindrical spaces of the two fastening cylinders which are connected with each other respectively at the same time. When each fastening cylinder sleeves the needle tip clamps, the needle tips are sealed by the needle tip clamps under the extrusion of the inner walls of the fastening cylinders.