A self-tightening elastic line ligator, comprising a body, a barrel and at least one elastic line, wherein the barrel comprises an inner barrel and an outer barrel, the elastic line is disposed along an outer wall of the outer barrel of the ligator, a front end of the elastic line form a size-adjustable loop loopingly disposed on an outer wall of a front end of the inner barrel, the ligator further comprises an elastic line automatic tensioning mechanism, wherein the elastic line automatic tensioning mechanism comprises: a line-retracting auto-connector, wherein a tail end of the elastic line is connected with the line-retracting auto-connector, a compression spring of which one end abuts the body and the other end abuts a free end of the line-retracting auto-connector, and a self-tightening trigger, which can keep abutting the free end of the line-retracting auto-connector with a resilient force, to keep the compression spring being compressed; wherein the elastic line automatic tensioning mechanism is configured such that when the tail end of the elastic line needs to be retracted, the self-tightening trigger can be pressed to release an abutment to the free end of the line-retracting auto-connector, and thus releases an abutment to the compression spring, and the line-retracting auto-connector is rebounded backward to tighten backward the elastic line under an action of a resilient force of the compression spring, thereby rapidly reducing a size of the loop at the front end of the elastic line. the barrel comprises an inner barrel and an outer barrel, the elastic line is disposed along an outer wall of the outer barrel of the ligator, a front end of the elastic line form a size-adjustable loop loopingly disposed on an outer wall of a front end of the inner barrel, the ligator further comprises an elastic line automatic tensioning mechanism, wherein the elastic line automatic tensioning mechanism comprises: a line-retracting auto-connector, wherein a tail end of the elastic line is connected with the line-retracting auto-connector, a compression spring of which one end abuts the body and the other end abuts a free end of the line-retracting auto-connector, and a self-tightening trigger, which can keep abutting the free end of the line-retracting auto-connector with a resilient force, to keep the compression spring being compressed; wherein the elastic line automatic tensioning mechanism is configured such that when the tail end of the elastic line needs to be retracted, the self-tightening trigger can be pressed to release an abutment to the free end of the line-retracting auto-connector, and thus releases an abutment to the compression spring, and the line-retracting auto-connector is rebounded backward to tighten backward the elastic line under an action of a resilient force of the compression spring, thereby rapidly reducing a size of the loop at the front end of the elastic line. a line-retracting auto-connector, wherein a tail end of the elastic line is connected with the line-retracting auto-connector, a compression spring of which one end abuts the body and the other end abuts a free end of the line-retracting auto-connector, and a self-tightening trigger, which can keep abutting the free end of the line-retracting auto-connector with a resilient force, to keep the compression spring being compressed; wherein the elastic line automatic tensioning mechanism is configured such that when the tail end of the elastic line needs to be retracted, the self-tightening trigger can be pressed to release an abutment to the free end of the line-retracting auto-connector, and thus releases an abutment to the compression spring, and the line-retracting auto-connector is rebounded backward to tighten backward the elastic line under an action of a resilient force of the compression spring, thereby rapidly reducing a size of the loop at the front end of the elastic line.