Abstract: Entomopathogenic fungi are used as bio-insecticides to control insect pests in agricultural and forest ecosystem. Their ecological adaptability in field was directly interrelated to control efficiency and constancy. To ensure a good control result, it is required for the fungal strains with a strong ability of field survival as well as the high virulence against the target insects. This paper summarized ecological adaptability of entomopathogenic fungi including diversity of species and distribution, relationships with insects and plants, population dynamic and so on. The review paper provides better ecological understanding on entomopathogenic fungi as key biological control agents, and benefits strategy choice of biocontrol application in the future.