A packer, which is configured to pack the bottom of a gap between a foundation pile and a sleeve, comprising: a clamp assembly, which can be sleeved on the foundation pile and is connectable with the bottom of the sleeve; and a cantilever assembly, which comprises a plurality layers of cantilever units stacked on the inner side of the clamp assembly and in the vertical direction, each cantilever unit comprises cantilever members annularly and densely placed at intervals on the inner side of the clamp assembly, each cantilever member comprises a fixed end and a cantilever end, the fixed ends are connected with the clamp assembly, the cantilever ends are configured to resist on the foundation pile, and wherein in use the length value of each cantilever member is not smaller than the difference value between the inner radius of the sleeve and the outer radius of the foundation pile; characterized in that the clamp assembly comprises a plurality of segments, and the segments are connected to each other to form an annular structure; wherein each segment comprises: a bottom plate, which is provided with an end plate at both ends; a fixed plate, which is arranged on the bottom plate, and the fixed plate is connectable with the sleeve; a mounting plate, which is arranged on the bottom plate, and the mounting plate is provided with mounting holes for mounting the cantilever members at intervals along the length direction of the bottom plate: and a limiting plate, which is arranged on the bottom plate, and the limiting plate is configured to limit the movement of the cantilever members; wherein the cantilever member is a single steel wire, the fixed end of the single steel wire is provided with an upsetting head, and the size of the upsetting head is larger than that of the mounting hole or wherein the cantilever member is a U-shaped steel wire, and the fixed end of the U-shaped steel wire is penetrated and fixed on two mounting holes; wherein the surface of the cantilever member is painted with paint or grease; wherein optionally the cantilever member is nylon wire or a composite member of steel wire and rubber. a clamp assembly, which can be sleeved on the foundation pile and is connectable with the bottom of the sleeve; and a cantilever assembly, which comprises a plurality layers of cantilever units stacked on the inner side of the clamp assembly and in the vertical direction, each cantilever unit comprises cantilever members annularly and densely placed at intervals on the inner side of the clamp assembly, each cantilever member comprises a fixed end and a cantilever end, the fixed ends are connected with the clamp assembly, the cantilever ends are configured to resist on the foundation pile, and wherein in use the length value of each cantilever member is not smaller than the difference value between the inner radius of the sleeve and the outer radius of the foundation pile; characterized in that the clamp assembly comprises a plurality of segments, and the segments are connected to each other to form an annular structure; wherein each segment comprises: a bottom plate, which is provided with an end plate at both ends; a fixed plate, which is arranged on the bottom plate, and the fixed plate is connectable with the sleeve; a mounting plate, which is arranged on the bottom plate, and the mounting plate is provided with mounting holes for mounting the cantilever members at intervals along the length direction of the bottom plate: and a limiting plate, which is arranged on the bottom plate, and the limiting plate is configured to limit the movement of the cantilever members; wherein the cantilever member is a single steel wire, the fixed end of the single steel wire is provided with an upsetting head, and the size of the upsetting head is larger than that of the mounting hole or wherein the cantilever member is a U-shaped steel wire, and the fixed end of the U-shaped steel wire is penetrated and fixed on two mounting holes; wherein the surface of the cantilever member is painted with paint or grease; wherein optionally the cantilever member is nylon wire or a composite member of steel wire and rubber. a bottom plate, which is provided with an end plate at both ends; a fixed plate, which is arranged on the bottom plate, and the fixed plate is connectable with the sleeve; a mounting plate, which is arranged on the bottom plate, and the mounting plate is provided with mounting holes for mounting the cantilever members at intervals along the length direction of the bottom plate: and a limiting plate, which is arranged on the bottom plate, and the limiting plate is configured to limit the movement of the cantilever members; wherein the cantilever member is a single steel wire, the fixed end of the single steel wire is provided with an upsetting head, and the size of the upsetting head is larger than that of the mounting hole or wherein the cantilever member is a U-shaped steel wire, and the fixed end of the U-shaped steel wire is penetrated and fixed on two mounting holes; wherein the surface of the cantilever member is painted with paint or grease; wherein optionally the cantilever member is nylon wire or a composite member of steel wire and rubber.