Due to geological and engineering factors, there exist difficulties with the performance of horizontal wells in sulfur gas reservoirs. In this study, an experiment is conducted on the performance of a horizontal well in a sulfur gas reservoir using a multifunction injection and production system for horizontal wells, with results verified by numerical simulation. Eight experiments are undertaken, including three for the influence of heterogeneity, three for the influence of drawdown pressure, and two for the influence of wellbore pressure drop. Results indicate that the inflow profile of the horizontal well in the experiment agrees well with the numerical simulation. Further experiments are conducted to investigate the effects of formation heterogeneity, drawdown pressure, and wellbore pressure drop on horizontal well performance. Results show that (1) greater heterogeneity means greater fluctuation in gas distribution along the horizontal well. The recovery factor become higher with the permeability differential decrease. (2) There is found a critical drawdown pressure at which a stable supply of gas can be achieved. Meanwhile, at the first stage, the main reservoir gas supply (B5) hold the largest permeability with a short duration; at the second stage, the other cores become the main source of gas supply. (3) Wellbore pressure drop makes gas distribution along the horizontal well gradually decrease from heel to toe. The results of this study can be used to guide completion optimization and production system adjustment.