A knitting needle, provided for a needle groove of a front or back needle bed of a flatbed knitting machine, and cooperative with another knitting needle in a corresponding needle groove of a back or front needle bed, wherein the knitting needle comprises: a hook; a latch, provided at a back side of the hook, and rotatable to close the hook; a shaft, comprising a stem and a shank arranged in sequence in a back portion of the hook, the shank being wider than the stem; a recessed first transfer portion, formed at a joint of the stem and the shank; a recess, provided in one side of the shaft; a flat spring set on a bottom surface of the recess, having a front portion bent outward in a length direction of the shaft to form a protrusion and a back portion fixedly connected to the bottom surface of the recess by welding to form a fixed connecting end; and a hook insertion slot, formed by an inner cavity between the protrusion and the bottom surface of the recess; characterized in that: the flat spring is provided with a recessed second transfer portion; the flat spring is further provided with a deformation surface located between a back side of the protrusion and a front side of the fixed connecting end; the deformation surface and the protrusion are not exposed outside the recess, or the deformation surface and the protrusion have a portion exposed outside the recess, wherein the portion exposed outside the recess is elastically pressed into the recess by the needle groove or is suitable to be located in a depression at a corresponding side of the needle groove; and during loop transfer, when a hook of another knitting needle in the corresponding needle groove is inserted into a position between the flat spring and the shaft through the hook insertion slot, and moves to a position between the deformation surface and the bottom surface of the recess, the deformation surface is configured to be elastically deformed to drive the protrusion to expand outward, such that a loop hung on the recessed first transfer portion and the recessed second transfer portion is stretched. a hook; a latch, provided at a back side of the hook, and rotatable to close the hook; a shaft, comprising a stem and a shank arranged in sequence in a back portion of the hook, the shank being wider than the stem; a recessed first transfer portion, formed at a joint of the stem and the shank; a recess, provided in one side of the shaft; a flat spring set on a bottom surface of the recess, having a front portion bent outward in a length direction of the shaft to form a protrusion and a back portion fixedly connected to the bottom surface of the recess by welding to form a fixed connecting end; and a hook insertion slot, formed by an inner cavity between the protrusion and the bottom surface of the recess; characterized in that: the flat spring is provided with a recessed second transfer portion; the flat spring is further provided with a deformation surface located between a back side of the protrusion and a front side of the fixed connecting end; the deformation surface and the protrusion are not exposed outside the recess, or the deformation surface and the protrusion have a portion exposed outside the recess, wherein the portion exposed outside the recess is elastically pressed into the recess by the needle groove or is suitable to be located in a depression at a corresponding side of the needle groove; and during loop transfer, when a hook of another knitting needle in the corresponding needle groove is inserted into a position between the flat spring and the shaft through the hook insertion slot, and moves to a position between the deformation surface and the bottom surface of the recess, the deformation surface is configured to be elastically deformed to drive the protrusion to expand outward, such that a loop hung on the recessed first transfer portion and the recessed second transfer portion is stretched. the flat spring is provided with a recessed second transfer portion; the flat spring is further provided with a deformation surface located between a back side of the protrusion and a front side of the fixed connecting end; the deformation surface and the protrusion are not exposed outside the recess, or the deformation surface and the protrusion have a portion exposed outside the recess, wherein the portion exposed outside the recess is elastically pressed into the recess by the needle groove or is suitable to be located in a depression at a corresponding side of the needle groove; and during loop transfer, when a hook of another knitting needle in the corresponding needle groove is inserted into a position between the flat spring and the shaft through the hook insertion slot, and moves to a position between the deformation surface and the bottom surface of the recess, the deformation surface is configured to be elastically deformed to drive the protrusion to expand outward, such that a loop hung on the recessed first transfer portion and the recessed second transfer portion is stretched.