Abstract: [Purpose/Significance] The differentiation, combination and fusion of knowledge are the driving force to stimulate scientific innovation and promote the development of science.This paper is concerned with the causal mechanism between boundary-spanning knowledge and citation counts based on knowledge combination perspective, which is of great significance for knowledge diffusion research. [Design/Methodology] Using propensity score matching, based on 2,860 papers of 5 journals in Scientometrics field during 2011-2015, and their backward as well as forward citation records, this research examines the impact of boundary-spanning papers on citation counts from the knowledge topic level. [Findings/Conclusion] The research results show that boundary-spanning has a positive effect on the citations of papers. Papers with a high degree of boundary-spanning may be cited about nine times more than papers with a lower degree boundary-spanning. The balance and common interval indicate the validity and reliability of the matching results. [Originality/Value] This paper reveals the internal relationship between the boundary spanning feature of papers and their citation counts, which provides necessary empirical support for exploring the flow of interdisciplinary knowledge and explaining the evolution of knowledge.

Key words: Boundary-spanning, Causal inference, Citations, Propensity score matching, Interdisciplinary, Knowledge diffusion