Abstract: The trend of development of natura1 sciences in this century is from the very small (particle physics)—the very large (cosmology)—the very complex (science of complexity). The studies of “complexity” are characterized by the trend of the times of scientific development and belong to fundamental researches with foreseeing, exploring and innovation. The author puts foreward the proposition of “Complexity and Self-Organized Criticality of Solid Earth System” in the light of: (1)the science of complexity studies the mechanisms of emergence of complexity and is the science of 21st century，and in combination with (2) the inherent fundamental attributes of complexity and self-organized criticality of the solid earth system. By the proposition we try to cogitate from a new viewpoint the ancient yet even-new solid earth system. The author abstracts the fundamental problem of the solid earth system from the essence of the generalized geological systems and processes，advances its three major basic theoretical problems and proposes the methodology of researches on the complexity of the earth system in which holism is dominant and reductionism is subordinate and macrophysics complemented with microphysics. “Complexity and Self-Organized Criticality of Solid Earth System” is one of the great scientific problems underlying our national economic increase, social progress and geosciences development. The study of this problem would become a growing point in the development of geosciences in the 21st century, causing it to make breakthrough in its advance and bringing along the development of many related disciplines concurrently.