In order to address the limitations of conventional Be (beryllium) windows, particularly their susceptibility to low-energy X-ray interference and poor thermal stability, SiC (silicon carbide) was proposed as a novel window material. A combined methodology incorporating Monte Carlo simulations and finite-element analysis was employed to investigate its X-ray transmission performance and heat-load capacity. The transmission ratio, peak-to-background ratio, and total peak ratio of the exit spectra were evaluated for Be and SiC windows with different thicknesses. This evaluation aimed to assess their ability to block low-energy X-rays while transmitting high-energy components. Transient thermal simulations were conducted to determine the maximum tolerable heat flux for SiC windows. The results indicate that SiC windows exhibit superior peak-to-background and total peak ratios compared to Be windows. For a 1.0 mm-thick SiC window, the peak-to-background ratio reaches 985.16%. Increased window thickness improves heat-load capacity, while prolonged operation reduces the maximum permissible power. The allowable tube currents are 0.08, 0.05, 0.03 mA for pulse durations of 5, 10, 20 s, respectively. It is concluded that a SiC window with a thickness of 1.0 mm provides an optimal balance between spectral performance and thermal management in 35 kV miniature end-window X-ray tubes.