The present invention provides a side coupled optical fiber for stripping high power cladding light. The side coupled optical fiber comprises a passive optical fiber, a coreless optical fiber and a low refractive index coating layer. Two ends of the passive optical fiber and the coreless optical fiber are separated, and the middle parts are arranged in parallel. The refractive index coating layer is arranged outside the parallel parts of the passive optical fiber and the coreless optical fiber. The coreless optical fiber is doped with a background loss impurity. Loss is introduced through doping the impurity in the coreless optical fiber. Due to an optical fiber coupling effect, the cladding light in the passive optical fiber is slowly coupled into the coreless optical fiber, thus loss converted from the loss is not accumulated in a short distance but is uniformly distributed on an optical fiber axial direction. The invention also provides a preparation method of the side coupled optical fiber for stripping high power cladding light.