In recent years, informal mechanism of technology transfer has attracted significant attention due to its flexible and open mechanisms. However, the existing research of informal technology transfer lacks systematic organization and review. Focusing on the theme of “informal technology transfer”, this study utilizes CiteSpace visualization technology to conduct a quantitative analysis of 161 selected articles from the WOS (Web of Science) and CNKI (China National Knowledge Infrastructure) databases, covering the period from 2001 to 2023. The study clarifies the connotation of informal technology transfer, presents the research hotspots, analyzes the mechanisms and pathways of informal technology transfer, and provides an outlook on emerging trends and research opportunities. Firstly, through a literature review, this paper discovers that the connotation of informal technology transfer has not been unified domestically and internationally. However, it can be distinguished from the perspectives of interpersonal interaction, contractual agreements, and transfer agents. Secondly, through textual analysis of existing research, this paper finds that studies related to informal technology transfer cover informal organizations, informal institutions, personal relationships, informal networks, the digital age, the digitalization of enterprises, and internal network structures. Thirdly, the research focus on informal technology transfer has evolved from initially revealing the operational relationships of informal organizations and institutions within and outside organizations to investigating the impact of “informal” factors in the context of the digital age. In addition, this study constructs an analytical framework for the implementation mechanisms and pathways of informal technology transfer, considering process orientation and the influence of internal and external driving factors on different key stakeholders’ involvement. Finally, the paper discusses future research directions for informal technology transfer, aiming to provide references for further in-depth studies in this field.