Abstract: The world is undergoing profound changes unseen in a century" is an important conclusion made by Xi Jinping in 2018 that has stirred up a thousand waves. This is an important summary and judgment of the world pattern and its changes and development trends and situations. The world situation is the main background factor facing China's development. How to understand the concept of "profound changes unseen" will greatly influence or even determine how China will respond and its countermeasures. We must look for the deep connotation of the concept in the history beyond a century. Now the development situation and situation summarized by this concept have become extremely obvious and increasingly fast. This "change" is still just the beginning, and there is still a long way to go between the large-scale main game and the final outcome. It also has a room for countermeasures. Its future development is a kind of “chemical change” which is uncertain, unstable, non-linear and irrational. Only a scientific, continuous, and advancing countermeasure to control, manage, and assist can effectively cope with this "profound change unseen in the world in a century."