Student teachers are invaluable educational assets, especially in digital transformation. The online collaborative reflection ability (OCRA) is crucial for their teaching careers and has always been challenging. There is a pressing need for new collaborative learning strategies to enhance student teachers' OCRA and improve the quality of future teaching professionals. This study introduces socially shared regulation of learning (SSRL) scaffold to enhance OCRA and utilizes a mixed-methods (quali-quantitative) approach in a quasi-experimental design involving 48 student teachers over a semester. Both the questionnaire survey and epistemic network analysis (ENA) results indicated that the SSRL scaffold significantly enhanced student teachers' OCRA levels. Under the influence of SSRL, the reflection levels of student teachers advanced to higher tiers, with reflection content focusing on critical and contextual reflection. Furthermore, the analysis elucidated how SSRL affected student teachers' OCRA in different stages of online learning activities. Suggestions about task design and intervention plans for each stage of SSRL are provided to teachers and learning designers to uncover better and cultivate OCRA.