In the history of China's emergence of the Party, Mao Zedong was the first to consciously put forward the idea of seeking truth from facts. He first used the concept of "ideological line" in his letter to Lin Biao on June 1929. In this letter, he made a philosophical analysis of some wrong views in the party of Gongsijun at that time, pointing out that we are materialists, and we must examine everything from both historical and environmental aspects before we can get the truth. The existence of some wrong ideas is just a "historical knot" and "the last struggle on a wrong ideological line in history" But Mao Zedong's "ideological line" here refers to the cognitive line. 1930 in may, Mao Zedong clearly put forward the ideological line in his article against bookishness. Mao Zedong put forward: "* * * party member's ideological line should create a new situation from the practice of struggle". To this end, he also put forward the slogan of "no right to speak without investigation" and firmly believed that "leaving the actual investigation will produce idealistic class evaluation and idealistic work guidance, so the result is either opportunism or blindness." At that time, Mao Zedong took the investigation and study based on the reality of China as the basis of the party's ideological line, and consciously used the historical theory of dialectical materialism to guide the party's practical work.