Abstract: Mao Ze-dong's strategy theory of "the three worlds" is based on world situation and the great changes of the basic contradictions in the world,especially on the fact that there is a vast intermediate region between the great two poles of USA and USSR.The main points of this theory are:USA and USSR belong to the first world,practise hegemonism,and are the great enemies of the people in the world.The developing countries in the great areas of Asia,Africa,Latin America and other regions belong to the third world, constitute the main force to fight against colonialism,imperialism and hegemonism.The second world includes those developed capitalist countries that lay between the two super powers of USA and USSR on the one hand and the great many third world countries on the other hand,with which the third world countries can make an alliance in fighting against hegemonism.Mao Ze-dong's theory of the three worlds openes up a great space for China's diplomacy in the world,provides a theoretical ground for the world people to fight against hegemonism and thus makes a great contribution to world peace and the progressive human cause.