The necessity of concerted endeavors to safeguard and rejuvenate the Taihu Basin environment is of the utmost importance in the context of the integrated, high-quality development of the Yangtze River delta region. It is of great significance in enlightening the policy-making of the regional environmental cooperation and enriching the theory of collaborative environmental governance. The present study sets out to systematically study how to coordinate the interests of local main bodies to carry out cross-boundary synergistic paths of environmental governance actions. The paper employs a qualitative research method of case study, and through the long-term tracking and investigation of the Suzhou-Jiaxing transboundary water governance practices, it constructs a comprehensive pathway framework for transboundary collaborative environmental governance from the aspects of synergistic content demand and realization guarantee, based on the theory of collaborative governance. The study has identified institution, technology and action as the key synergistic contents of the transboundary environmental collaborative governance path. The synergistic implementation of these three factors is identified as an important guarantee to promote the success of transboundary collaborative environmental governance. The Suzhou-Jiaxing grassroots government's pioneering introduction of a joint river-chief system can be regarded as a governance model through institutional synergy, with a deepening and expansion of the content of action-oriented synergy in the order of institutional cost and implementation cost from low to high. This has been demonstrated to be effective in improving the quality of the transboundary river environment. However, the content of technical synergy is less substantial, which limits the improvement of transboundary collaborative environmental governance capacity. The coordination of local stakeholders' interests in transboundary environmental cooperation is identified as the key driving force for the development of its cooperative governance path. The results obtained reveal the focus of synergistic contents, the characteristics of time-sequence combination and the synergistic effect of local subjects in the process of transboundary collaborative environmental governance. The findings of this study are of good practical guiding value.