R & D diffusion is the basis and prerequisite for the diffusion of technological innovation, especially the R & D diffusion effect of center city in science and technology plays an important role on the technological progress of surrounding region. This paper describes the systems theory of R & D diffusion and conducts both qualitative and quantitative analysis upon evaluation variables influencing of R & D diffusion capacity. Also from both domestic and foreign point of view, citing Beijing as an example, this paper conducts an empirical research on the diffusion effects of R & D applying the extended CH model. The results showed that there is a lag of domestic R & D input and diffusion effects brought by foreign R & D diffusion effects of FDI, and the diffusion effects of FD I will inhibit the domestic technology innovation and diffusion to some extent.