The invention relates to a low-attenuation and large-effective-area single-mode 
optical fiber. The single-mode 
optical fiber comprises a core layer and wrapping 
layers and is characterized in that the 
radius r1 of the core layer is 4.8 micrometers-6.5 micrometers, and the relative 
refraction index 
delta1 of the core layer is 0.10%-0.24%; the core layer is wrapped with the inner wrapping layer, the sunk inner wrapping layer, the transitional outer wrapping layer and the outer wrapping layer in sequence from inside to outside; the 
radius r2 of the inner wrapping layer of the 
optical fiber is 8.5 micrometers-15 micrometers, the relative 
refraction index 
delta2 of the inner wrapping layer of the optical 
fiber is -0.3%--0.05%, the 
radius r3 of the sunk inner wrapping layer is 14 micrometers-22 micrometers, the relative 
refraction index 
delta3 of the sunk inner wrapping layer is -0.45%--0.2%, the radius r4 of the transitional outer wrapping layer is 35 micrometers-50 micrometers, and the relative refraction index delta4 of the transitional outer wrapping layer is -0.25%--0.05%; the outer wrapping layer is a pure 
silica glass layer. The attenuation parameter of the optical 
fiber is decreased; through reasonable design of 
all fiber core layer sections of the optical 
fiber, the optical fiber has an effective area larger than or equal to 100 square micrometers. The overall performance parameters of cutoff 
wavelength, bending loss and chromatic dispersion of the optical fiber are good in an application 
wave band, and a multilayer stepped sunk wrapping layer structure is adopted for the section of the optical fiber and well reduces the bending loss of the optical fiber.