Metasynthesis is a new contribution of Qian Xuesen to modern science and technology in recent 20 years. It is one of the main achievements in the third creation upsurge in his life. Starting from analyzing historical background for the formation of metasynthesis,and quoting a large number of already published data, the article textually criticises and expounds the practising basis and practical process of the abstraction and formation of metasynthesis and the subsequent enrichment and development. Then the article points out its chief characteristic and its great effect and meaning for the development of modern science and technology.