Brand green extension of enterprises refers to launching new green products with the support of the market influence from mature brands. It can not only help enterprises quickly and effectively occupy the green market and convey its environmental protection concepts such as saving resources, cleaner production, recycling materials and so on to the whole society, but also help enterprises establish an eco-friendly green image and deliver messages that they are positively undertaking environmental protection responsibility. Therefore, there exist certain limitations when applying the classic research paradigm of brand extension to understand consumers’ response mechanism of brand green extension. Furthermore, the academic community has begun to pay attention to the influence of individual psychological attributes of consumers, especially mindset, on consumers’ evaluation of brand extension in recent years. Existing studies argue that diverse consumer mindset will result in diverse consumer response to brand extension. Relevant research further demonstrates that when starting global processing mindset, consumers respond more positively to brand prototype extension than brand exemplary extension; when starting local processing mindset, consumers respond more positively to brand exemplary green extension than brand prototype extension. Based on the above argument, this study discusses the effects of congruence between the brand green extension type and consumer mindset on consumer response, and tests the mediating role of environmental legitimacy perception in the influence mechanism above and the moderating role of green trust in the influence mechanism above through three experiments. Experiment 1 was conducted among undergraduate students. The result shows that when starting global processing mindset, consumers respond more positively to brand prototype green extension; when starting local processing mindset, consumers respond more positively to brand exemplary green extension. Experiment 2 was conducted among MBA and EMBA members to verify the conclusion of Experiment 1 and test the mediating role of environmental legitimacy perception. The result shows that congruence between the brand green extension type and consumer mindset affects consumer response through environmental legitimacy perception. Experiment 3 used different experiment materials to test the moderating role of green trust. The result shows that for those consumers with a high level of green trust, congruence between the brand green extension type and consumer mindset has a positive influence on consumer response; for those consumers with a low level of green trust, the effects of congruence between the brand green extension type and consumer mindset do not exist. The conclusions of this study provide a new perspective for brand extension research, and also provide theoretical support for enterprises to develop efficient green marketing strategies.