The invention relates to a single-mode fiber with ultralow damping and a large effective area. The single-mode fiber comprises a core layer and a wrapping layer. The single-mode fiber is characterized in that the radius R1 of the core layer is 5.5 to 7.5 [mu]m; a relative refractivity difference deltan1 is -0.02 to 0.10%; an inner packaging layer, a recessed inner packaging layer, an auxiliary outer packaging layer and an outer packaging layer successively warp the core layer from inside to outside; the radius R2 of the inner packaging layer of the fiber is 14-17 [mu]m; the relative refractivity difference deltan2 of the inner packaging layer is -0.40 to -0.15%; the radius R3 of the recessed inner packaging layer is 15-19 [mu]m, and the relative refractivity difference deltan3 is -0.8 to -0.3%; the radius R4 of the auxiliary outer packaging layer is 35-52 [mu]m, and the relative refractivity difference deltan4 is -0.50 to -0.20%; and the relative refractivity difference deltan5 of the outer packaging layer is -0.50 to -0.20%. The single-mode fiber has advantages of large effective area, low attenuation, relatively high bending loss and relatively high dispersion performance. The fiber has a low enough cutoff wave length of the finished cable.