A hollow-core anti-resonant fiber is proposed with low confinement loss in infrared band. The cladding tube is a semicircular semi-elliptical splicing structure. The full vector finite element method is used for the simulation. The semi-minor axis of the semi-elliptical tube is equal to the radius of the semicircular tube. A semi-circular tube and a semi-elliptical tube are spliced to form a semi-circular semi-elliptical cladding tube. The negative curvature and the positive curvature are changed by improving the structure parameters of the tube. The purpose of this paper is to study the loss characteristics of the positive and negative curvature of the cladding tube, and to design a low loss hollow core anti-resonant fiber applied in the 1.5~3.0 μm band. The results show that the effect of limiting loss is better when the negative curvature decreases and the positive curvature increases. The lowest confinement loss is 8.22×10^-2 dB/km at the wavelength of 2.1 μm when the semi-circular tube is close to the core and the elliptical tube is far away from the core, as well as the circular radius r_y=25 μm, the semi-major axis of the ellipse r_x=65 μm, the semi-minor axis of the ellipse r_y=25 μm.