Abstract: On the basis of reinterpreting alienation as separation, Arendt put forward the concepts of earth alienation and world alienation, and revealed a possible causal chain between the development of modern technology and the emergence of ecological crisis. As Arendt pointed out, earth alienation and world alienation damage the natural ecology in different ways. This difference reveals the ambivalent attitude of modern people towards natural ecology, and behind it, the ambivalent understanding of human existence conditions. Although Arendt's theory of alienation is unique in revealing the contradictions in modern society and in understanding the causes of modern ecological crisis, it can not help people step out of ecological crisis in practice because of her denial of human nature.