Abstract: Systems science and systems engineering, as a new science and technology domain in modern science and technology, is developing rapidly, and showing greater and greater vitality. QIAN Xuesen is recognized as the pioneer and founder of systems science and systems engineering in China. His whole innovation process from systems thinking to systems practice has made pioneering contributions at different levels from engineering, technology, science to philosophy. These achievements and contributions have very important scientific value and practical significance. 
Presenting QIAN Xuesen’s contribution in systems science and practice, this paper elaborates the development and application of systems science and systems engineering.