With the widespread use of social media platforms, human-technology interactions in platform environments provide a new perspective for understanding digital inequality. This article constructs a conceptual framework through the analytical tool of “platform affordance” to reveal how the mutual construction of humans and technology extends the boundaries of digital inequality beyond structural factors. The framework considers the positive sequential relationship between technology-efficacy and self-efficacy, highlighting their dominant role in promoting stratified uses and outcomes on social media platforms. Using survey data from Sina Weibo users in China, we find that users’ perceptions of the location of the feature’s icon and methods of operation shape online content creation through their perceived capabilities and needs, resulting in an unequal distribution of digital capital. On the one hand, platform affordance weakens the mechanisms that reproduce social inequality; it does so by revealing the fundamental role of interaction between technological properties and personal expectations in guiding online activities. On the other hand, platform affordance also reshapes how social structural factors operate; it does so by triggering moderating effects of personal and positional characteristics on the relationship between technology-efficacy and self-efficacy.