A new type of photonic crystal fiber with three layers of rectangular air holes in the cladding was designed and studied. The optimal structure of the fiber was obtained using finite element method modeling. On this basis, the key parameters of the optical fibers at varying wavelengths were modeled and studied. The results show that the optical fiber can support 46 modes of stable transmission in the wavelength range of 1 300~1 700 nm. In this band, the effective refractive index difference between the adjacent modes of photonic crystal fibers is greater than 10⁻⁴. The purity is 98.8%, the effective mode field area exceeds 6.4 × 10⁻¹¹ m², the nonlinear coefficient is less than 2.24 × 10⁻³, and the maximum numerical aperture is 0.1180. Compared with the existing photonic crystal fibers, the new fiber has more transmission modes, less transmission loss, and is made from easily accessible materials, making it promising for future optical fiber communications.