Dragon fruit (Hylocereus polyrhizus) constitutes an important economic industry in Guizhou Province, China; however, in recent years, stem rot in this region has become increasingly severe. Moreover, the pathogens responsible for stem rot in Guizhou and their sensitivity to fungicides remain elusive. Therefore, in this study, we aimed to determine the causative pathogens of stem rot in this region and analyze their sensitivity to fungicides. Twenty-four isolates were obtained from diseased tissues, from which H-4 and H-5 were selected and confirmed as pathogens. Based on the morphological characteristics of macroconidia, microconidia, and colony morphology, the polygenic phylogenetic tree constructed using internal transcribed spacer, elongation factor 1-alpha, and retinol-binding protein-2 gene fragments, along with carbon source metabolism using FF microplates, the two pathogens were identified as Fusarium oxysporum and F. concentricum respectively. In addition, the in vitro toxicity of eight fungicides against both pathogens were measured based on mycelium growth rate. The results showed that 75% trifloxystrobin·tebuconazole exhibited the strongest inhibitory effect on both isolates, with concentration for 50% of maximum effect values of 0.1262 µg/mL and 0.1385 µg/mL, respectively. This study identified two Fusarium spp. as the causative pathogens of stem rot in dragon fruit, with F. concentricum being reported for the first time, and demonstrated the best fungicide for them. These findings hold significant potential for guiding the effective treatment of stem rot in dragon fruit in Guizhou, China.