<p>This research investigates the effect of residential mobility on subjective well-being (SWB) and the underlying mechanism involved. Using a nationwide longitudinal survey covering 2014–2020 and a staggered difference-in-differences identification strategy, this study reveals that residential mobility causally reduces movers’ SWB by 0.122 on a 5-point scale. The effect remains robust when controlling for various fixed effects and potential confounders. This study argues that social comparison is the mechanism through which residential mobility undermines movers’ SWB: when movers compare themselves to locals in their host cities, their self-assessed social status decreases, which reduces their SWB. We regress self-assessed social status on residential mobility and find that residential mobility causes a reduction of 0.134 in individuals’ self-assessed social status on a 5-point scale. Heterogeneity analyses buttress this mechanism: people who move to more developed regions suffer a greater loss of SWB, and younger adults, who have a greater social comparison orientation, also suffer a greater loss of SWB. This study is the first to provide nationwide longitudinal evidence that residential mobility undermines movers’ SWB in China. It is also one of the few studies that empirically confirms the role of social comparison in the relationship between residential mobility and SWB.</p>