This study investigates the drag coefficient of spherical fuel elements in the vertical lifting pipelines of the fuel handling system for high-temperature gas-cooled reactors (HTGR) under high blockage ratio conditions. Focusing on the drag coefficient Cd of an in-line array of three spheres under steady flow conditions. Using the k-ω SST turbulence model, numerical simulations were performed to analyze incompressible flows around the spheres at various distances s between sphere centroid. Helium was employed as the working fluid for the simulations in this study. The simulations, conducted using FLUENT 2022R1, examined the relationship between drag coefficients, inlet flow velocity, and sphere spacing. Results reveal that the drag coefficients of the downstream two spheres are nearly identical under any inlet velocity and spacing condition. Additionally, for a given spacing S, the drag coefficient of the leading sphere shows a specific functional relationship with those of the downstream spheres. Furthermore, the drag coefficient of the leading sphere is found to correlate with that of a single sphere under equivalent flow conditions. These findings provide theoretical insights into the aerodynamic behavior of multi-sphere systems in confined spaces, offering further engineering improvements for the start-up transport of multi-sphere arrays.