The invention discloses a treadle-operated pre-toilet-flushing valve. A horizontal pipe (2) and a vertical pipe (3) are metal tubes, the inner diameters of the horizontal pipe (2) and the vertical pipe (3) are same, the axis of the horizontal pipe (2) and the axis of the vertical pipe (3) are perpendicular to each other, and a pipe cap (4) is arranged at the upper end face of the vertical pipe (3). A valve rod (6) is installed at the upper end of a ball valve (1), and the valve rod (6) penetrates through the pipe cap (4) and can move up and down in a hole of the pipe cap (4). A support (11) is fixed to the horizontal pipe (2) and is sequentially provided with a supporting column (8), a supporting pin (9) and a torsion spring (15). One end of a foot lever (7) penetrates through a square hole in the upper end of the supporting column (8) and is hinged to the valve rod (6), the other end of the foot lever (7) is sequentially provided with two pedals including a pre-flushing pedal (12) and a flushing pedal (13). The pre-toilet-flushing valve is simple in structure and convenient to operate, has a squatting pan pre-flushing function, and does not waste many water resources.