[目的/意义]旨在探明社交媒体用户从众信息分享行为的成因与作用机制，为用户信息行为引导、舆情信 息监管和网络信息传播机制优化提供理论参考。[方法/过程]从行为者、客观刺激物和情境或关系层面分别引入 信息甄别自我效能、信息源可信度和主观规范三个自变量，构建理论模型，通过问卷调查采集262份有效样本数 据，并利用偏最小二乘法结构方程模型（PLS-SEM）对数据及模型进行分析与验证。[结果/结论]信息甄别自我效 能、信息源可信度和主观规范均对社交媒体用户从众信息分享行为产生显著正向影响，且主观规范影响最大。此 外，信息甄别自我效能能够负向调节主观规范对社交媒体用户从众信息分享行为的影响，但并不能调节信息源可 信度对社交媒体用户从众信息分享行为的影响。本研究揭示了社交媒体用户从众信息分享行为的成因与作用机 理，为人们理解用户从众信息行为提供了参考，为社交媒体“刷屏”现象提供了合理解释，为三度归因理论的应用 提供了范例与场景，也为相关方的服务优化、政策制定等提供了策略启示，具有一定的理论和实践意义。

 [Purpose/significance] The purpose of this paper is to explore the cause and mechanism of social media herd information sharing behavior, and to provide a theoretical reference for the guidance of user information behavior, the supervision of public opinion information and the optimization of network information dissemination mechanism. [Method/process] This paper introduces the variables of self-efficacy in information screening, subjective norms, and information source credibility from the aspects of actors, situations or relationships and objective stimuli, and con? structs a theoretical model by combing the relationship between variables. Then, 262 valid data were collected by ques? tionnaire, and the partial least squares structural equation model (PLS-SEM) was used for data analysis and model veri? fication. [Result/conclusion] Self-efficacy in information screening, subjective norms and information source credibili? ty all have a significant positive impact on herd information sharing behavior of social media users, and in which the im? pact of subjective norms is the greatest. In addition, self-efficacy in information screening can negatively regulate the impact of subjective norms on herd information sharing behavior of social media, but cannot adjust the impact of infor? mation source credibility on herd information sharing behavior of social media. This study reveals the cause and mecha? nism for herd information sharing behavior of social media users, provides a reference for people to understand users' herd information behavior, provides a reasonable explanation for the phenomenon of "screen brushing" in social media, provides an example and scene for the application of triple degree attribution theory, and also provides strategic enlight? enment for service optimization and policy formulation of relevant parties, which has certain theoretical and practical significance.