This invention discloses a method for segregation purifying insect pathogenic fungi thalline from suscepted insect bloodlympha. It is prepared through steps as follows: deal with blood cell of suscepted insects with a series of enzymes to destroys and removes their germ plasms; finally seperate and purify to get the products. Adopt the achieved pathogenic fungi thalline to extract DNA and mRNA, which has no insect germ plasm pollution according to PCR and RT-PCR verification. The DNA and mRNA extracted can be used to construct gene library, it also lays solid foundation for further uncovering entomogenous fungi invading mechanism.