In order to effectively control Heliothis assulta Guenée, its regularity of occurrence and forecasting were studied on the basis of years’ records collected from each monitoring point in tobacco planting areas in Hunan. The results showed that the actual number of generations of Heliothis assulta Guenée agreed with that of predicted ones; the population of the first generation was always larger than that of the following generations. Generally, more moths’ emerged earlier than usual foreshadows its prevalence in that year; the major factors relevant to forecast were microenvironment of attraction, natural enemies, frost, attractive plant