G.657 fibers are regarded as the first choice for local net and access net such as Fiber to the home (FTTH) systems for their excellent property of bend-insensitive loss. Therefore, this kind of fiber is highly discussed in recent years. A method of fully synthetic process was introduced to fabricate G.657 fibers, and the relation between attributes of fiber and the size of core a and cladding b difference of refractive index of core (Δ1) and cladding (Δ2) were discussed in detail. As a result, when a is between 3.5～4.0 μm, b is between 0.5～1.9 μm, Δ1 between 0.0034～0.0045 and Δ2 between -0.0006～0 fibers complying with the standard of ITU.T G.657.A are obtained, while a is between 2.8～3.2.0 μm, b is between 0.8～2.1 μm, Δ1 between 0.0058～0.0072 and Δ2 between -0.0016～-0.0008 fibers complying with the standard of ITU.T G.657.B are obtained. Structures of the fibers are simple without special dips, grooves or holes, and therefore easy to fabricate, spread and use.