With the growing environmental awareness and the introduction of store brands in online platforms, product competition between the manufacturer and e-tailer is fierce. The impact of store brand development on manufacturer and retailer profits is widely debated. In this study, we attempt to clarify the competitive dynamics between the manufacturer and e-tailer by examining the interaction between store brands and green technology in different sales modes. We find that high store brand quality does not always attract the e-tailer to introduce the store brand. This phenomenon occurs because higher store brand quality triggers greater green technology improvement. Although agency selling can mitigate the double marginalization of the national brand, it increases the difficulty for the store brand to enter the market. Interestingly, while the manufacturer and e-tailer have opposite preferences for sales modes, both the manufacturer and e-tailer prefer reselling when the percentage fee is moderate. In particular, this tendency of the manufacturer increases with the improvement of green technology. Finally, from the perspective of environmental performance, sales quantity and green technology improvement are crucial influencing factors. In most cases, reselling produces less environmental pollution. Our results reconcile some discrepancies between theory and practice on the supply chain impact of green technology and store brand interactions.