A new structure of hexahedron core with the heptagonal shape of cladding regions based on photonic crystal fiber (Hx-PCF) is presented of this research work. The finite element method (FEM) and perfectly matched layers (PML) based COMSOL Multiphysics has been used to design this photonic crystal fiber (Hx-PCF) with appropriate design parameters. The fiber discloses the high relative sensitivity (RS) which stand 86.32%, 88.36%, and 84.25%, and low confinement losses along with the value of 5.60 × 10–08, 6.60 × 10–08 dB/m, and 5.55 × 10–08 dB/m for three chemicals such as Ethanol (n = 1.354), Benzene (n = 1.366) and Water (n = 1.330), respectively at operating region of 1 THz (THz). Furthermore, some other optical characteristics such as an effective mode index (EMI), effective area (EA), total power fraction (TPF), effective material loss (EML), V-Parameter are also analyzed along through essential graphic outputs. So, the results show the strong potential of this suggested Hx-PCF fiber for bio-medical areas to detect biochemicals and also industrial areas for identifying many types of chemicals by sensing procedure in the terahertz (THz) waveguide system.