Abstract: "The Letter of the CPC Central Committee to All Comrades in Shangcheng County" is an inner-party document that integrates praise, criticism and instructions issued to the local party organizations in Shangcheng County in the name of the CPC Central Committee in the early days of the Agrarian Revolutionary War. This inner-party document has played an important role in consolidating and expanding the fruits of victory achieved by the Shangcheng Uprising, publicizing the international and domestic situation and the Party's principles and policies after the 6th National Congress of the Communist Party of China, and effectively solving the problems and disputes existing in the local Party organizations in Shangcheng. However, due to the influence of the "Third Period Theory" of the Communist International, the relevant instructions of the CPC Central Committee in the book to all comrades in Shangcheng County have obvious "left" signs and certain one-sidedness, which have brought certain negative effects on the revolutionary work of Shangcheng and the construction of local party organizations in Shangcheng.