Diaporthe species are associated with Citrus as endophytes, pathogens, and saprobes worldwide. However, little is known about Diaporthe as endophytes in Citrus grandis in China. In this study, 24 endophytic Diaporthe isolates were obtained from cultivated C. grandis cv. “Tomentosa” in Huazhou, Guangdong Province in 2019. The nuclear ribosomal internal transcribed spacer (ITS), partial sequences of translation elongation factor 1-α (tef1), β-tubulin (tub2), and partial calmodulin (cal) gene regions were sequenced and employed to construct phylogenetic trees. Based on morphology and combined multigene phylogeny, eleven Diaporthe species were identified including two new species, Diaporthe endocitricola and D. guangdongensis. These are the first report of D. apiculata, D. aquatica, D. arecae, D. biconispora, D. limonicola, D. masirevicii, D. passifloricola, D. perseae, and D. sennae on C. grandis. This study provides the first intensive study of endophytic Diaporthe species on C. grandis cv. tomentosa in China. These results will improve the current knowledge of Diaporthe species associated with C. grandis. The results obtained in this study will also help to understand the potential pathogens and biocontrol agents and to develop a platform in disease management.