In this paper the corresponding relationship between the migrating south of the nomadic nationalities in North China and the climatic changes is studied. In the warm period the nomadic nationalities dwelt in north of the Great Wall lived together in peace with the agricultural nationality dwelt in the Central Plains (comprising the middle and lower reaches of the Yellow River). However the in cold period the nomadic nationalities lauched an all-out offensive on agricultural world because the forage grass withered, the water source had dried up in the prairie. At the same time in the Central Plains the agricultural world was also hit by the cold climate, the agriculture drop in production, the economy depressed, the national power declined. Thus, they cannot sustain the blows from nomadic world. Because the period of cold climate got longer and longer, and the degree of cold climate got bigger and bigger in recent 2000 years, the extent of migrating south of the nomadic nationalities became larger and larger. In fact as early as the Han Dynasty the theory of “Interaction between heaven and man’s world” had been founded. The theory is the concentrated expression of feedback machanism of climate ecology-economy-society.