High mode discrimination and large mode area in fibers are key technical challenges for the generation and transmission of high-power radially polarized field (RPF) laser. Based on this, a novel method for the design of a radially polarized field fiber is proposed. By introducing a circularly symmetrical radially distributed thermal stress field into the core of the fiber, a radial birefringence effect can be realized in the core, which effectively breaks the degeneracy between polarization modes in conventional optical fibers. The effective index difference among TM₀₁, TE₀₁, and HE₂₁ modes is of the order of 10 ^-4. This allows the TM₀₁ radial polarization mode to be separated. In addition, a large mode area design for the TM₀₁ mode field can be achieved by using the proposed RPF fiber.