The invention provides a root-anchor system reinforcing ecological slope protection method for a fill slope. Firstly, multiple lines of reinforcing steel bar anchor rods are embedded in the surface of an existing hard side slope in the slope direction, concrete slab anchor heads are poured at the positions of the tops, exposed out of the surface of the hard side slope, of the anchor rods, and a fixed pulley with the rotation direction in the downhill direction is installed on each concrete slab anchor head; meanwhile, a banket retaining wall is constructed at the position of the toe of the hard side slope; and a pull rope is wound around each fixed pulley, one end of each pull rope is perpendicularly stretched to the designed slope surface height of the fill, and the other end of each pull rope is then wound around the other fixed pulleys, in the same line with the corresponding fixed pulley and located below the corresponding fixed pulley in the slope direction, so as to be embedded in and fixed to the back face of the retaining wall, the end, corresponding to the last anchor rod in each line of anchor rods in the slope direction, of the corresponding pull rope is directly embedded in and fixed to the back face of the retaining wall, filling is conducted till the designed slope surface height, concrete lattice girders are constructed, and the tip, perpendicularly stretched to the fill slope height, of each pull rope is anchored after being pulled and tensioned. By means of the method, deep reinforcing and ecological protection of the fill slope can be achieved.