Abstract: The boundaries of athletes' freedom of expression in modern sports are examined using the Olympic Charter and its related rules and regulations as the object of study. It argues that there should be in modern sports a need to restrict athletes' freedom of expression in terms of the sports autonomy, therefore it summarizes the three basic principles of restriction, that is, the principles of "political neutrality", "non-discrimination" and "non-commercialization". In addition, the IOC should continue to adhere to the principles of "political neutrality", and to improve the principle of "non-discrimination" in order to achieve its goal of building a peaceful and better world against the contemporary background of the profound changes unseen in a century. The national countermeasures are also proposed from three levels of helping the legitimate expression of athletes, restraining improper expression of athletes from other countries, and scientifically formulating national sports policies related to freedom of expression.