One of the most challenging issues confronting social media operators is how to increase users’ activity and self-disclosure behaviour. However, more and more users are lowering their disclosures on social media, such as WeChat in China. Using social cognitive theory as a starting point while utilizing mobile instant messaging software WeChat as an example, this paper studies the dynamics that influence users’ self-disclosure behaviour on WeChat from two aspects: individual factors and environment factors. A structural equation model is used to verify a conceptual model. The results show that, firstly, mobile users’ self-disclosure behaviour on WeChat can be affected by both individual factors and environment factors. Specifically, individual factors, such as privacy concerns, negatively affect users’ self-disclosure behaviour, while environmental factors, such as social influences, positively affect users’ self-disclosure behaviour. More importantly, the research points to significant differences in self-disclosure behaviour between mobile users of different genders and ages. As such, the conclusions of this paper should provide key information for optimized operation of WeChat and other mobile information systems.