Litchi downy blight (Peronophythora Litchi Chen ex Lo) is one of the most important preharvest and postharvest diseases of Litchi. The effect of temperature, pH, light, carbon source and moisture on the mycelia growth, sporulation and sporangia germination of litchi downy blight was primarily studied. For the mycelial growth of the pathogen of the litchi downy blight, the range of temperatures was 12-32℃, the optimum being 28-30℃, and the range of pH was 3-10, the optimum being 6-8. For the sporulation, the range of temperatures was 12-32℃, the optimum being 26-30℃, and the range of pH was 3-10, the optimum being 5-6. For the sporangium germination, the range of temperature was 10-34℃, the optimum being 20～26℃，and the range of pH value was 3-10, the optimum being 5-6. The treatment of darkness with fluorescent or alternative fluorescent light did not have significant effect on the mycelial growth, sporulation or sporangium germination. Only in free water, the sporangium was able to germinate. The starch, sucrose, glucose and maltose could promote the mycelial growth.