The invention relates to a double-position adjustable self-keeping fast floating ball valve. A valve base, a movable valve element, a valve element lever arm, a valve rod supporting rotating shaft, afloating ball lever, a magnetic force self-keeping mechanism, an upper limit floating ball, a lower limit floating barrel and an upper and lower limit adjusting floating barrel pull rod are included;when the water level is lowered to be lower than the lower limit floating barrel, liquid in the lower limit floating barrel changed into gravity, so that the total gravity borne on a lever is larger than the magnetic keeping attracting force, and the movable valve element connected to the lever is driven to perform fast valve opening; before the liquid level ascends to that the upper limit floating ball is submerged, the total gravity is still larger than buoyancy, and the valve open state is maintained; when the liquid level ascends to that the upper limit floating ball generates a rated buoyancy, the floating ball lever is driven to ascend, and ascends till a magnetic keeping mechanism generates an attracting force, the valve closing force is doubled, and the valve closing process is accelerated so that a water inflow valve can be fast closed; and in the valve closed state, before the liquid level descends to that the lower limit floating barrel is exposed, the valve closed state iskept due to the magnetic attracting force, and therefore double-position adjustable self-keeping fast valve opening and closing of the floating ball valve can be achieved, and the problems of shocking, quivering, abrasion and the like are avoided.