Abstract: Sinicization of Marxism is an inevitable requirement to break the shackles of subjectivism, especially dogmatism, and to correctly solve China’s problems. During the Yan’an period, Mao Zedong not only put forward the proposition of the sinicization of Marxism, but also devoted himself to promoting the process of the era of sinicization of Marxism. The rectification movement is a key part of eliminating the harm of subjectivism, sectarianism and the three evils of the Party, and promoting the close integration of the basic principles of Marxism with China’s reality. Through rectification, the whole Party has improved its understanding of Marxism and strengthened the consciousness of linking theory with practice. Investigation and research is a bridge and an intermediary to correctly understand “facts” and scientifically “seek truth”, and to successfully realize the close integration of Marxist theory with China’s national conditions. Through investigation and research, the whole party has improved its understanding of China’s national conditions and strengthened the firmness of linking theory with practice. Driven by the combined forces of the sinicization of Marxism, the rectification movement and investigation and research, the ideological line of seeking truth from facts was finally established in the Yan’an period.