Abstract: "Basically achieving socialist modernization" is a landmark proposition with both diachronic and synchronic dimensions. Its formation and development have drawn on the theoretical explorations of classical Marxist writers concerning socialism and social development, as well as the Communist Party of China’s continuous deepening of its understanding of the laws governing socialist modernization. The proposition has been further enriched through the implementation of the 14th Five-Year Plan and the strategic planning for the 15th Five-Year Plan. Theoretically, a moderately prosperous society in all respects constitutes its practical foundation; the term "basically" defines its stage-specific orientation; three consecutive Five-Year Plan periods provide its temporal structure; the Five-Sphere Integrated Plan and the Four-Pronged Comprehensive Strategy form its practical framework; and systems thinking constitutes its principal methodological requirement. The Fourth Plenary Session of the 20th CPC Central Committee made a series of new arrangements for basically achieving socialist modernization by accurately defining its historical stage, systematically summarizing its guiding principles, formulating its principal objectives, coordinating its driving mechanisms, and deepening the understanding of its salient features. Guided by the spirit of the Fourth Plenary Session and grounded in the historical position of the 15th Five-Year Plan, a theoretical examination of the meaning and contributions of this proposition is significant for advancing the building of a strong country and national rejuvenation, deepening the understanding of the laws governing socialist modernization, and broadening the pathways toward modernization for human society.