The scientific background that grey systems theory come into being, the astonishing progress that grey systems theory has made in the world of learning and its widely employment in many scientific areas is presented in this paper. The mysteries for continual growth of grey systems theory were revealed by the trends of system sciences and uncertainty system theory needs of social practice, and by simplicity principles of scientific theory, scientific method and scientific model, etc. This paper with a certain reference value for found or develop a new branch of learning.