A small bending radius single-mode optical fiber with compatibility with conventional G.652 optical fibers, comprising a core gradient layer and a germanium-doped core layer arranged concentrically, and a first wrapping layer, a second wrapping layer and a third wrapping layer arranged concentrically from the inner to the outer, wherein a first transition layer is arranged between the germanium-doped core layer and the first wrapping layer, a second transition layer is arranged between the first wrapping layer and the second wrapping layer, and a third transition layer is arranged between the second wrapping layer and the third wrapping layer; characterized in that the difference of relative index of refraction of the core gradient layer is Δn1, which is realized through an equation: Δn1 = a 1 (x 1 + x 1 2 + x 1 3) + b 1, wherein x 1 is the distance from any point within the core gradient layer to the axis of said layer, a 1 is gradient factor of the core gradient layer, ranging from 0.5% to 2%, and b 1 is gradient stability factor of the core gradient layer, ranging from 0 to 0.2%; the difference of relative index of refraction of the first transition layer is Δn3, which is realized through an equation: Δn3 = b 3 (1 - a 3 x 3 2) 0.5, wherein x 3 is the distance from a concentric circle around the centre of an optical fiber at any point within the first transition layer to the outer edge of the germanium-doped core layer, and a 3 and b 3 are transition factors, both ranging from 0.3% to 0.8%; the difference of relative index of refraction of the second transition layer is Δn5, which is realized through an equation: Δn5 = a 5 x 5 2 + b 5, wherein x 5 is the distance from a concentric circle around the centre of an optical fiber at any point within the second transition layer to the outer edge of the first wrapping layer, and a 5 and b 5 are transition factors, a 5 ranging from -1.0% to -0.3%, and b 5 ranging from 0 to 0.1%; and the difference of relative index of refraction of the third transition layer is Δn7, which is realized through an equation: Δn7 = a 7 x 7 2 + b 7, wherein x7 is the distance from a concentric circle around the centre of an optical fiber at any point within the third transition layer to the outer edge of the second wrapping layer, and a 7 and b 7 are transition factors, a 7 ranging from 0.1% to 0.4%, and b 7 ranging from -1.3% to -0.3%. the difference of relative index of refraction of the core gradient layer is Δn1, which is realized through an equation: Δn1 = a 1 (x 1 + x 1 2 + x 1 3) + b 1, wherein x 1 is the distance from any point within the core gradient layer to the axis of said layer, a 1 is gradient factor of the core gradient layer, ranging from 0.5% to 2%, and b 1 is gradient stability factor of the core gradient layer, ranging from 0 to 0.2%; the difference of relative index of refraction of the first transition layer is Δn3, which is realized through an equation: Δn3 = b 3 (1 - a 3 x 3 2) 0.5, wherein x 3 is the distance from a concentric circle around the centre of an optical fiber at any point within the first transition layer to the outer edge of the germanium-doped core layer, and a 3 and b 3 are transition factors, both ranging from 0.3% to 0.8%; the difference of relative index of refraction of the second transition layer is Δn5, which is realized through an equation: Δn5 = a 5 x 5 2 + b 5, wherein x 5 is the distance from a concentric circle around the centre of an optical fiber at any point within the second transition layer to the outer edge of the first wrapping layer, and a 5 and b 5 are transition factors, a 5 ranging from -1.0% to -0.3%, and b 5 ranging from 0 to 0.1%; and the difference of relative index of refraction of the third transition layer is Δn7, which is realized through an equation: Δn7 = a 7 x 7 2 + b 7, wherein x7 is the distance from a concentric circle around the centre of an optical fiber at any point within the third transition layer to the outer edge of the second wrapping layer, and a 7 and b 7 are transition factors, a 7 ranging from 0.1% to 0.4%, and b 7 ranging from -1.3% to -0.3%.