To make coordinated efforts to protect and restore the Taihu Basin environment is the important content 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 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 adopts the qualitative research method of case study and through the long-term tracking and investigation of the Su-Jia transboundary water governance practices, we construct a comprehensive pathway framework for transboundary environmental collaborative governance from the aspects of synergistic content demand and realization guarantee, based on the theory of collaborative governance. The study has found that: Institution, technology and action are the key synergistic contents of the transboundary environmental collaborative governance path, and the synergistic implementation of the three is an important guarantee to promote the success of transboundary environmental collaborative governance. The joint river-chief system pioneered by the Su-Jia grassroots government is more of a governance model through institutional synergy, deepening and expanding the content of action-oriented synergy in the order of institutional cost and implementation cost from low to high, which effectively improves the transboundary river environmental quality, but the content of technical synergy is less substantial, which limits the improvement of transboundary environmental collaborative governance capacity. Coordination of local stakeholders’ interests around transboundary environmental cooperation is the key driving force for the development of its cooperative governance path. The results reveal the focus of synergistic contents, the characteristics of time-sequence combination and synergistic effect of local subjects in the process of transboundary collaborative environmental governance, which are of good practical guiding value.