The massive influx of Chinese migrants into post-Soviet Russia has created among other consequences a rich mythology and a system of stereotypes. An important component of this complex is the concept of "Chinese expansion" aimed at economic and cultural development of the Russian Far East and Siberia with their subsequent annexation. A key role in this concept is played by the idea of "demographic expansion". The article is devoted to the analysis of its significant constituent -the thesis of "marriage expansion" as an instrument of nonviolent and invisible invasion through assimilation, dissolution of the Russian population in the Chinese demographic dominance. This mythologeme and rhetoric based on it have been regarded by some politicians as an effective tool of political manipulation and struggle for power. However, the marriage statistics of the Far Eastern and Siberian cities show a little number of mixed marriages. The corresponding calculations of scientists are now needed not so much to fight against this myth as to study complex problems of intercultural interactions in human relations. Having studied the idea of "marriage expansion", we could identify some mechanisms of myth-making. The result shows, in particular, that the distinction between the mythological and scientific consciousness with mutual diffusion observed is not as rigid and specific as the interstate border. Naturally, myths are the scientific analysis object. But often they act in the form of scientific knowledge, authoritative in the society. Moreover, mythological representations can penetrate into real scientific research; all it takes is only to neglect the sacred for historians principle of "criticism of sources".