For a fiber having an inverted parabolic distribution as its refractive index distribution, adding a low refractive index layer between the core and the fiber cladding can create an improved novel fiber. This novel fiber can accommodate a high-order orbital angular momentum (OAM) mode field. Calculation of the normalized cutoff frequency showed that the novel fiber can support 9 fiber modes and accommodate the OAM modes with a topological charge of 3. According to the calculations, the effective refractive index differences for the degenerate modes of LP11 and LP21 both reach 2.1×10 -4, and the effective refractive index difference between the degenerate modes of LP31 reaches 10 -3. The vector modes were effectively decoupled and the degenerative separation effect of the higher order modes was improved. Finally, the influence of the low refractive index layer's distribution on the optical fiber transmittable vortex light mode was analyzed.