In today’s changing world, all kinds of problems are plaguing people’s thinking. Why is there a conflict between Russia and Ukraine? Why did the Soviet Union continue to expand and interfere in the internal affairs of other countries? What is the difference between Roma in Europe and Hakka in China? What impact does the change in global temperature have on the development of human society? Why did the United States lose in Vietnam and Afghanistan? This book uses the knowledge of thermodynamics to explore the problems of social systems. We can even apply the theory of social thermodynamics to the animal world to see why the polygamous societies of lions are so markedly different from the monogamous societies of wolves. By quantifying some important parameters, the social thermodynamic system can be used to analyze the relationship between social pressure, social temperature and social space, and obtain corresponding critical parameters to judge the possibility of phase transition in social systems. At the same time, the state of the social system can be judged according to entropy and free energy. The main focus of this book is sociology, so the mathematics used is relatively simple.