In this research work, a novel design of octagonal cladding with two elliptical cores in photonic crystal fiber (O-PCF) is studied for application in the terahertz (THz) frequency regime. There exists five layers octagonal figure in circular air holes (CAH) of cladding region with two elliptical shapes of core area are proposed in this research work. The O-PCF features of the fiber have been explored using full vector finite element method (FEM) with perfectly match layer (PML) boundary condition that have been used to confine the light inside the core region properly. Some supplementary significant fiber features for THz signal spread with low confinement loss, high core power fraction, scattering loss and single-mode PCF circumstances of the fiber have also been considered. Simulated results exhibition compares to the low effective material loss (EML) of 0.0153 cm−1, larger effective area of 5.95 × 10–8 m2, core power fraction of 79%, a low confinement loss and scattering loss such as 3.36 × 10–14 dB m−1 and 1.25 × 10–10 dB km−1 respectively at 1 THz frequency regime. To shorten design and smooth fabrication, only circular shaped air holes have been employed. Due to its promising characteristics, the proposed SM-OPCF waveguide provides efficient transmission of broadband terahertz signals. The suggested excellent designed of O-PCF can be used mostly for in nano-optics, biomedical signal processing, optical amplification, SONET and others communication areas.