A tie-down tension enhancer for in-situ tightening of an installed tie down having a locking mechanism. The tension enhancer generally includes a body having openings for transverse insertion and removal of a line or strap as well as longitudinal movement of the line or strap within the body. A cinch is provided and disposed on the body for engaging the line or strap upon longitudinal movement of the line or strap in one direction and a line or strap mechanism is provided and spaced apart from the cinch for enabling pulling of the line or strap past the cinch for providing further tension to the existing tie down.