2.3 μm Tm-doped fiber lasers can be widely used in environmental gas detection, medical imaging, non-invasive blood glucose measurement and other fields. The 2.3 μm and 1.9 μm dual-wavelength laser cascaded amplification technology based on Tm-doped fiber can effectively suppress the amplified spontaneous emission and parasitic lasing in the 1.9 μm band, and achieve high-power 2.3 μm laser output. Further improvement of 2.3 μm fiber laser power significantly depends on the development of large mode area single-mode Tm-doped fiber. Traditional core-cladding structure optical fiber has difficulty maintaining single-mode operation when the core diameter increases, resulting in degradation of the beam quality in laser system based on large-mode-area fiber. All-solid anti-resonant fiber has attracted widespread attention due to its properties on large mode area single-mode operation, wide transmission bandwidth, and flexible structural parameter design. Active fiber realized by doping rare earth ions in the fiber core has potential application in high-power fiber laser generation. A large mode area single-mode Tm-doped all-solid anti-resonant fiber with a core diameter of 40 μm was designed based on tellurite glass, and a 2.3 μm and 1.9 μm cascade fiber amplifier based on this fiber was numerically simulated in this paper.Comsol Multiphysics was used to build the fiber model, simulate fiber loss, get overlap integral, and design the anti-resonant fiber. Then, a numerical simulation model was built based on the rate equations of thulium ions and the power transmission equations of the amplifier, and was used in numerical simulation of the 1.9 μm and 2.3 μm dual-wavelength fiber amplifier based on the designed fiber.Based on the mode coupling between the high-order modes and the cladding mode, an anti-resonant fiber with fundamental mode loss less than 1 dB/m, while the loss of all high-order modes greater than 10 dB/m in the 1.8-2.5 μm band was demonstrated (Fig.3). The comparison of 2.3 μm single-wavelength amplification and 1.9 μm and 2.3 μm dual-wavelength amplification shows that injecting 1.9 μm seed light into the amplifier can effectively suppress amplified spontaneous emission in the 1.9 μm band during 2.3 μm laser amplification (Fig.4). Signal laser in 2.3-2.4 μm band can be efficiently amplified (Fig.6). The slope efficiency of the dual-wavelength laser amplifier based on the designed fiber is about 30.6% for 1.9 μm signal, and about 23.6% for 2.3 μm signal with pump power of 100 W, and the 2.3 μm signal can be amplified from 2 W to 24.8 W (Fig.7).A single-mode Tm-doped tellurite all-solid anti-resonant fiber with core diameter of 40 μm is designed, which achieves a fundamental mode loss of less than 1 dB/m in the 1.8-2.5 μm band, and all high-order mode losses are greater than 10 dB/m, ensuring the single-mode transmission of signal light in the 1.9 μm and 2.3 μm bands. The numerical simulation of the 1.9 μm and 2.3 μm dual-wavelength fiber amplifier based on the designed fiber shows that the parasitic oscillation of the Tm-doped tellurite fiber amplifier in the 1.9 μm band can be effectively suppressed by only using 0.2 W of 1.9 μm seed light, and tens of watts of 2.3 μm laser amplification can be achieved. It can be indicated that the designed fiber would exhibit good laser amplification performance in the wide band range of 2.3-2.4 μm. The design process of the active all-solid antiresonant fiber proposed in this paper can be applied to the design of large mode area active fiber in other wavelength bands, which can serve as a reference for the design of large mode area single-mode fiber used in high-power fiber lasers and amplifiers.