Climate advocacy serves as an effective strategy for encouraging the public to engage in climate actions. However, the consistency between climate advocates' words and deeds largely determines the effectiveness of climate advocacy. While the facilitating effects of word-deed consistency on public willingness to follow have been extensively examined, the potential diminishing effects of excessive word-deed consistency remain underexplored. Given that lacking understanding of the potential backfire may undermine the effectiveness of climate advocacy, we conducted two preregistered studies (N = 996) to investigate the inverted-U relationship between word-deed consistency and willingness to follow, along with the underlying mechanisms. Both studies revealed that word-deed consistency facilitated willingness to follow by increasing perceived credibility, similarity, moral threat and decreasing perceived hypocrisy when it was below a moderate level. Conversely, word-deed consistency diminished willingness to follow by decreasing perceived similarity when it exceeded a moderate level. Furthermore, Study 2 demonstrated that advocating for easy low-carbon behaviors can eliminate the diminishing effects of excessive word-deed consistency on willingness to follow. The present research contributes to a more comprehensive understanding of the relationship between word-deed consistency and willingness to follow and provides insight into effective climate advocacy.