People who believe that their socioeconomic status (SES) can be changed—with growth mindset or incremental implicit theory of SES—tend to have better psychological well-being. Nevertheless, it remains unclear on why growth mindset of SES benefits well-being. The present research aims to answer this question by investigating the longitudinal associations between mindset of SES and well-being (i.e. depression and anxiety) and a potential mechanism (i.e. self-esteem). We recruited 600 adults in Guangzhou, China, as participants in this study. Participants completed a list of questionnaires containing measures of mindset of SES, self-esteem, depression, and anxiety at three time points over the course of 18 months. The cross-lagged panel model showed that individuals holding a growth mindset of SES reported significantly lower depression and anxiety 1 year later, but the effect was not sustained later. More importantly, self-esteem accounted for the associations of mindset of SES with both depression and anxiety, such that individuals with growth mindset of SES had higher self-esteem, and in turn, demonstrated lower depression and anxiety over 18 months. These findings deepen the understanding of the salutary effects of implicit theories of SES on psychological well-being. Implications for future research and mindset-related interventions are discussed.