Mid-infrared fiber combiners have great potential in power and spectral combination. However, studies on mid-infrared transmission optical field distributions using these combiners are limited. In this study, we designed and fabricated a 7 x 1 multimode fiber combiner based on sulfur-based glass fibers and observed approximately 80% per-port transmission efficiency at 4.778 & mu;m wavelength. We investigated the propagation properties of the prepared combiners and explored the effects of transmission wavelength, output fiber length, and fusion deviation on the transmitted optical field and beam quality factor M2. Additionally, we assessed the effect of coupling on the excitation mode and spectral combination of the mid-infrared fiber combiner for multiple light sources. Our results provide an in-depth understanding of the propagation properties of the mid-infrared multimode fiber combiners, which may find applications in high-beam-quality laser devices.& COPY; 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement