Abstract: There are many factors which will affect the effectiveness of knowledge transfer within MNCs. Taking the American MNCs as the research targets, the impact of headquarters’ knowledge transfer abilities, motives, richness of explicit and tacit knowledge transferring channels on the effectiveness of knowledge transfer are mainly analyzed. Hofstede’s national culture model is also borrowed to mainly analyze the moderating effects upon the knowledge transfer effectiveness caused by the cultural differences on the two dimensions of power distance, and masculinity vs. femininity, and then the measures improving the effectiveness of cross-cultural knowledge transfer within MNCs are put forward.