This paper presents a study on the effective mode area and effective refractive index of a suspended-core photonic crystal fiber based on a Ge20Sb5Se75 chalcogenide with CS2-filled air holes, with the aim of applications in the mid-infrared region. By using Lumerical Mode Solutions, we investigated the effect of varying the structural parameters of the fiber on two polarization modes (TE00 and TE100) in the wavelength range of 1-5.5 µm. We demonstrate that the real part of the effective refractive index (R[neff]) can be tuned over a wide range by varying the w/rc ratio slot width and the wavelength, with values ranging from 2.2016 to 2.1889. In contrast, the effective mode area (Aeff) increases with both wavelength and slot width, with values ranging from 1.2692 to 1.1215 µm2 at 2050 nm. In addition, we compare our model with an unfilled sample, which exhibits lower values of both Aeff and Re[neff] compared to the CS2-filled SCF. These results provide a crucial foundation for the optimal design of Ge20Sb5Se75/CS2 fibers for nonlinear and mid-infrared transmission applications.