In his later years, Engels wrote To Conrad Schmitt (1890.8.5, 1890.10.27), To Joseph Bloch (1890.9.21-22), To Franz Merlyn (1893.7.14), To Walter Borgius (1894.1.25), To Paul Ernst (1890.2.5) six letters, through a comprehensive discussion of the decisive role of economic relations in the development of social history, a detailed discussion of the relative independence and reaction of ideology, and a special emphasis on the dialectics of historical materialism, demonstrating the scientific method of using historical materialism to study historical development and analyze historical phenomena, It further upheld, defended and developed the basic principles, theoretical content and dialectical essence of historical materialism. Engels’s six letters in his later years have inspired us to consciously safeguard the security of socialist ideology with a high degree of party spirit, to give the youth correct ideological education and guidance, to deeply understand the dialectics of historical materialism, and to adhere to practical application in china.