[Purpose/significance] Frequent privacy leakage incidents and increasingly complex privacy control strate⁃gies have exacerbated user privacy fatigue, and exploring the formation mechanism of social media users' privacy fa⁃tigue can provide a theoretical reference for user cognitive load relief, privacy anxiety debugging and effective privacy protection strategy formulation. [Method/process] Combining cognitive load, cognitive bias and CAC theory, the forma⁃tion mechanism model of privacy fatigue of social media users was constructed, and the partial least squares structural equation model and fuzzy set qualitative comparative analysis method were used for empirical test and configuration analysis. [Result/conclusion] In terms of cognitive factors, overconfidence positively affects optimism bias, informa⁃tion overload, social overload and system function overload all positively affect emotional exhaustion, and system func⁃tion overload also has a positive impact on negative neglect. In terms of emotional factors, emotional exhaustion, nega⁃tive neglect and optimistic bias all positively affect user privacy fatigue, and optimistic bias not only has a positive im⁃pact on emotional exhaustion and negative neglect, but also positively affects privacy fatigue under the mediating effect of the two. In terms of configuration effect, the two antecedent configurations of information overload and social over⁃load will trigger user privacy fatigue. In addition, there was no significant difference in the effect of control variables such as demographics on social media users' privacy fatigue.