The judgment of principal contradiction facing the society in the new era is based on the status of China's social productive forces and productive relations since the 18th CPC National Congress, and is in line with relevant theories of Marxism on the times. The principal contradiction facing Chinese society in the new era has the basic characteristics of practical, affinity to the people, periodic and developmental. The evolvement of principal contradiction facing the society in the new era shows that the current contradiction between social supply and demand has changed from the previous "quantity shortage" to "quality shortage". The essence of the evolvement is the change in the nature of principal contradiction facing human society in the new era. The evolvement of principal contradiction facing the society in the new era is the specific embodiment of "changes" and "invariability" in the CPC's theory of social principal contradictions. That is, the change of the specific form of contradiction has not changed the essence of the contradiction between supply and demand being still the principal contradiction facing the society, nor has it changed the basic national conditions and international status of China. In the new era, the formulation of policies must proceed from the current reality of China and not be divorced from the reality, and the theory of principal contradiction facing the society in the new era must be adhered to. The characteristics of principal contradiction facing the society in the new era and its solutions determine the characteristics and specific content of the basic strategy of the new era, and provide a theoretical basis for its smooth progress.