The results of a large number of implementation studies are not satisfactory. Most researchers interpret and analyze these unsatisfactory research findings from a methodological perspective with the scrutiny of the research design and implementation process. Few researchers have reflected on these results from a paradigmatic level. This paper firstly summarizes the research status of implementation science and teases out the mainstream paradigms of implementation research: positivism and constructivism. The positivist perspective focuses on the effectiveness of implementation strategies, and promotes the replicability and generalizability of research findings through various clinical trial designs with emphasis on the standardized interventions and implementation processes; constructivist perspective emphasizes the role of human beings, and promotes the power balance between researchers and knowledge users by building a long-term and stable partnership. It aims to facilitate facilitate knowledge users’ meaningful engagement in the whole implementation processes (such as the identification of research problem, development of implementation strategies, data analysis and interpretation, and dissemination of research findings etc.) and ensure the relevance and sustainability of research achievements. On this basis, this paper introduces the concept of complexity science by summarizing its origins, definition, the philosophical basis and the essence of healthcare from complexity science perspective, and puts forward the principles and methodologies of implementation research under the guidance of complexity science. The researcher argues that, different from efficacy and effectiveness researches, which aim to testify the effects of interventions in strictly or loosely controlled conditions, implementation research is to apply effective interventions into the real-world context which is full of complexity. Based on the perspective of complexity science, healthcare is a complex adaptive system, which has the characteristics of nonlinearity, openness, uncertainty, emergence and self-organization. It requires us to consider the implementation problems from a system level; embrace the creative opportunities brought by uncertainty; gain an in-depth understanding of the local context and organizational pattern; and promote the leading roles of knowledge users in the process of implementation, etc. Long-term and in-depth case study can be used as a methodology for implementation research from the complexity science perspective.

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