The aim was to provide the base for controlling the brown spot in Camellia reticulata f. simpex Sealy. Through field investigation, laboratory separation, identification and inoculation, the pathogen and susceptibility of brown spot disease of the Camellia reticulata f. Simpex Sealy were studied. The results showed phytopathogen was Pestalotiopsis guepini. The plant could be infected by inoculation with needle sting, and the symptom of infection could be observed in the greenhouse condition. The re-separation and identification from the infected leaf proved that it was the same pathogen as its original one. The temperature range for mycelia growth of Pestalotiopsis guepini was from 10 to 30℃, and the optimum temperature was 25℃. The sporulation temperature range was from 20 to 25℃, and the optimum was 25℃. For the conidial germination, the temperature range was from 15 to 30℃, the optimum being 28℃, and the range of pH was from 4 to 8, the optimum from 5 to 6. Thus, the Pestalotiopsis guepini had high pathogenic susceptibility to those plants with weak growth potential or wound. The study laid the foundation of etiology, infection cycle of and control system for brown spot disease of Camellia reticulata f. simpex Sealy.