A diving vest with adjustable buoyancy mainly has a back pad filled with a soft polyurethane gel body therein and disposed additionally on a back portion on an inner side of a regular vest; two left and right sides at the lower ends of the back pad extend respectively to form lashing waist bands; the protruding back pad leans against a human body's concave waist spine portion for obtaining a good ergonomic support and protecting the waist spine portion; the lashing waist band penetrates through a ring band on a waist bag of the vest thereby linking the waist bag to tightly lash a diver onto the vest. The lashing waist band lashes from the back pad as the beginning point such that it is more capable of tightly pulling the vest from the rear to the front for lashing the diver.