Abstract: The existing studies on the impact of external knowledge on creativity and innovative performance keep controversial. One important reason might be that in most studies actors’ cognitive ability has been ignored. Creative cognition theory and constructivism learning theory have pointed out that individual cognitive ability influence the relation between knowledge and creativity. However, no empirical study addresses this issue. This article explored the effect of research and development (R&D) employees’ knowledge assimilation capacity on the relationship between the strength of external knowledge searching and their innovative performance. Based on the survey paired-sample data of 207 R&D employees from 7 research organizations, the analysis results demonstrated that: 1) The strength of external knowledge searching had no significant effect on R&D employees’ innovation performance. 2) R&D employees’ knowledge assimilation capacity increased their innovative performance. 3) Assimilation capacity moderated the relationship between the strength of external knowledge searching and innovative performance. In the end, R&D management suggestions were discussed.