Abstract: Tsien H.S.'s thought of engineering sciences is a profound national innovation theory, which focuses on national science and technology policy, engineering education and overall knowledge system of science and technology. However, due to the confusion on the understanding of relevant terms and concepts, the thought has not played its due role in guiding innovative policies. On the basis of trying to clarify the etymology of engineering sciences, this paper clarifies the connotation and its position in the modern science and technology system, explains the role of engineering sciences in building a powerful country. We appeal to all sectors of society to carry forward Qian Lao's thought of engineering sciences, build a modern science and technology system focusing on engineering sciences, strengthen the education of basic theory of natural science and start the strong potential of engineering sciences in building a powerful country.