The theory of “three major differences” is an important part of the Marxist theoretical system. With Comrade Mao Zedong as their chief representative, Chinese Communists dialectically analyzed the contradictory nature, development trend and solutions of the “three major differences” in different societies, and explored how to narrow and eliminate the “three major differences” in socialist China which used to be economically and culturally lagging. The Chinese Communists, with Deng Xiaoping, Jiang Zemin and Hu Jintao as their chief representatives, have continued to explore ways to narrow the “three major differences”. They correctly studied and judged the development and trend of China’s “three major differences”, set the goal of reversing the widening trend in differences, and explored practical approaches to reduce differences. Chinese Communists, with Comrade Xi Jinping as the chief representative, propose in the new era that narrowing the “three major differences” must follow the path of socialism with Chinese characteristics and adhere to four cardinal principles. On the basis a correct understanding of objective laws, the Central Committee of the Communist Party of China, with Comrade Xi Jinping as the core, has led the whole party and the people of all groups in China to carry out great practice and has made great achievements in narrowing the “three major differences”.