The third to the forth century B.C.the nation of city was collapsed in Greece.People were in a turbulent situation without security.Religion,hunger and death threatened people's life.They were also wrapped in frightening.At this critical moment,Epicurus put forward his philosophy of atomic theory,which argued that the world was not created by God and could not be destroyed,individuals were free,friendship could improve safety feeling,moderation could settle short of supplies and make people happy,and people need not feel fear for the death.His theory looked like a good remedy and offered people the hope of cheer and happiness.