The key point of understanding the “post-truth” should not only rest on the pros and cons of emotion and fact, but also put the relationship between emotion and rationality into the long history and different political ecosystems, and give a reasonable orientation to the function of emotion to grasp the essence of the post-truth. Actually, public’s emotions, prejudices and ignorance are normal phenomenon in Western democratic elections. Although seemingly absurd, they have realized “emotional compensation” in the campaign, forming an “invisible” power decentralization mechanism and producing “the miracle of aggregation” effect. Even though the emotional expression in Chinese public opinion has some characteristics of “post-truth”, it is totally different from western logic. It stems from irrational emotional “forced” effect, and emotion is regarded as a kind of social resource that can be mobilized. Therefore, emotion is not the opposite of truth, it is a part of cognitive psychology, a component of rational system, and a resource of social mobilization and social integration. We need to examine the “hidden” function of emotions in a dialectical way to gain insight into humanity and grasp the law of “The Change” and “Unchange” in social and political ecology.