A single-mode optical fiber with ultra low attenuation and large effective area, comprising: a core layer and cladding layers, wherein the cladding layers comprises an inner cladding layer surrounding the core layer, a trench cladding layer surrounding the inner cladding layer, an auxiliary outer cladding layer surrounding the trench cladding layer, and an outer cladding layer surrounding the auxiliary outer cladding layer; wherein the core layer has a radius (r 1 ) in a range of 4.8 to 6.5 μm, and a relative refractive index difference (Δ n 1 ) in a range of -0.06% to 0.10%; wherein the inner cladding layer has a radius (r 2 ) in a range of 9 to 15 μm, and a relative refractive index difference (Δ n 2 ) in a range of -0.40% to - 0.15%; wherein the trench cladding layer has a radius r 3 in a range of 12 to 17 μm, and a relative refractive index difference (Δ n 3 ) in a range of -0.8% to - 0.3%; wherein the auxiliary outer cladding layer has a radius (r 4 ) in a range of 37 to 50 μm, and a relative refractive index difference (Δ n 4 ) in a range of - 0.6% to -0.25%; wherein the outer cladding layer is a pure silicon dioxide glass layer; characterized in that the core layer is a silicon dioxide glass layer co-doped with germanium fluorine and alkali metals, or a silicon dioxide glass layer co-doped with germanium and alkali metals, wherein a relative refractive index contribution (Δ Ge ) of the germanium in the core layer is in a range of 0.02% to 0.10%, and the doping quantity of the alkali metals is in a range of 50 to 5000ppm; and that the alkali metals in the core layer comprise one or more of lithium, sodium, potassium, rubidium, cesium and francium alkali metal ions. a core layer and cladding layers, wherein the cladding layers comprises an inner cladding layer surrounding the core layer, a trench cladding layer surrounding the inner cladding layer, an auxiliary outer cladding layer surrounding the trench cladding layer, and an outer cladding layer surrounding the auxiliary outer cladding layer; wherein the core layer has a radius (r 1 ) in a range of 4.8 to 6.5 μm, and a relative refractive index difference (Δ n 1 ) in a range of -0.06% to 0.10%; wherein the inner cladding layer has a radius (r 2 ) in a range of 9 to 15 μm, and a relative refractive index difference (Δ n 2 ) in a range of -0.40% to - 0.15%; wherein the trench cladding layer has a radius r 3 in a range of 12 to 17 μm, and a relative refractive index difference (Δ n 3 ) in a range of -0.8% to - 0.3%; wherein the auxiliary outer cladding layer has a radius (r 4 ) in a range of 37 to 50 μm, and a relative refractive index difference (Δ n 4 ) in a range of - 0.6% to -0.25%; wherein the outer cladding layer is a pure silicon dioxide glass layer; characterized in that the core layer is a silicon dioxide glass layer co-doped with germanium fluorine and alkali metals, or a silicon dioxide glass layer co-doped with germanium and alkali metals, wherein a relative refractive index contribution (Δ Ge ) of the germanium in the core layer is in a range of 0.02% to 0.10%, and the doping quantity of the alkali metals is in a range of 50 to 5000ppm; and that the alkali metals in the core layer comprise one or more of lithium, sodium, potassium, rubidium, cesium and francium alkali metal ions. <EOS>