Abstract: The stack configuration of solid oxide fuel cell （SOFC） significantly influences its overall performance. This study investigated a metal-free interconnect stack structure consisting of 128 flat-tube SOFC （FT-SOFC） units through both experimental testing and three-dimensional simulations. The dual-layer cell arrangement allows the spacing between the lower-row cells to function as natural air manifolds, promoting secondary flow distribution. This enhanced temperature uniformity and discharge performance in the upper-row cells. To address issues of large internal temperature gradients and sinusoidal temperature fluctuations along the stack width, an optimization strategy based on air manifold design and cell group spacing was proposed. Simulation results indicated that the optimized structure reduced the maximum cross-sectional temperature difference by approximately 20 ℃ and increased the overall operational temperature by around 20 ℃. The improved thermal uniformity offers valuable guidance for the structural design and integration of large-scale SOFC stacks.