Tacit knowledge has become the most important strategic resource for enterprises to obtain sustainable competitive advantage in the era of knowledge economy driven by information technology. Knowledge management theory believes that the transmission of tacit knowledge is an effective way to acquire and innovate knowledge for employees in the enterprise. The construction of knowledge in the organization relies heavily on the propagation of tacit knowledge between demanders and users considering characteristics of organizational cognition. A few new propagation paths begin to emerge with the rapid development of information and communication technology. WeChat group has become an important platform for tacit knowledge transmission in an enterprise and among enterprises. WeChat group is a virtual social platform that uses social network technology to achieve efficient communication and collaboration among employees within the enterprise. It eliminates the obstacles of time and space. WeChat group gathers employees together in a virtual way to communicate and mine the ideas of the group. It also realizes the online communication and dissemination of knowledge in the enterprise. Most of the users in WeChat group are employees within the same enterprise compared with weak online social networks such as Weibo. The users in a WeChat group have a higher sense of community identity and more trust among them. Their communication is more active and direct. A WeChat group gradually forms a cultural circle with a clear topic. Therefore, the knowledge transfer in the WeChat group is more interactive and efficient. The employees are more likely to get work-related tacit knowledge in their WeChat group. Furthermore, employees can understand the social network and knowledge of other employees by observing the topics and commenters of the exchanges in WeChat group. It can promote the recognition and retrieval of knowledge by employees. It also improves the efficiency of knowledge dissemination. In summary, WeChat group has become an important channel for tacit knowledge dissemination within enterprises. However, few studies have explored the law and characteristics of tacit knowledge spreading in WeChat Group. In-depth study of the mechanism of tacit knowledge transmission in WeChat group is of great significance for the realization of knowledge dissemination within the enterprise. In view of this, this study constructs the model of tacit knowledge propagation in WeChat group based on the theory of complex network propagation dynamics. We study the propagation mechanism of tacit knowledge in WeChat group and explores the corresponding promotion strategy of tacit knowledge transmission from the perspective of complex network. We analyze the established dynamic model and the threshold conditions for distinguishing whether a kind of tacit knowledge propagates in a WeChat group are derived. The transmission threshold R0 in this study is identical to the basic reproductive number in infectious disease dynamics. The tacit knowledge transmission threshold indicates that when all users in the WeChat group are users without tacit knowledge, the maximum number of other new users with this tacit knowledge by a knowledge owner in the average time required to forget the knowledge at the initial moment of tacit knowledge propagation. When R0>1, the tacit knowledge will propagate in the WeChat group; when R0<1, this tacit knowledge gradually disappears in the WeChat group. This study concludes that the knowledge transmission threshold is always a finite number by analyzing the influence of the degree distribution of the WeChat group on the propagation threshold. The following conclusions can be drawn from our research: (1) The threshold is always a finite number related to the user’s willingness to share knowledge and the ability to absorb knowledge. It is also related to the average and the second moment of the network. It can be seen from the above conclusion that all users in the WeChat group do not need to have tacit knowledge sharing intention or tacit knowledge absorption ability at the same time. Tacit knowledge will spread in the WeChat group as long as the number of tacit knowledge owners with shared willingness and the number of absorbing tacit knowledge recipients at the same time reach the corresponding critical values. Therefore, the administrator can realize the sharing of tacit knowledge in the WeChat group in a shorter time and at a lower cost according to the threshold condition. (2) Results also show that the network structure of WeChat group has a significant impact on tacitknowledgetransmission.The topology of the online social network composed of users’ communication in WeChat group has an important impact on tacit knowledge transmission. First, increasing the ratio of the second order moment to the average degree of the network can increase the threshold. It can lead to that tacit knowledge spreads faster in a scale-free network and the final scale of transmission are larger. The spreading speed is faster in scale-free network than in homogeneous network. The final size and the transmission threshold are larger in scale-free network than in homogeneous network. Therefore, if the difference between the number of communication times in unit time among the users is greater and then the final propagation scale is larger and the propagation speed is faster in the WeChat group. It can be seen from the above conclusion that appropriately changing the number of exchanges in the user’s unit time can promote the spread of tacit knowledge in the WeChat group. Managers can select some users with more average communication times per unit time and encourage them to interact with other users. It can increase the difference between the number of exchanges in unit time among the users. That is, the heterogeneity of the network degree distribution is increased. It can increase the final scale of tacit knowledge dissemination in WeChat groups and reduce the time to reach the final scale of knowledge transmission. (3) It is concluded that the number of knowledge owners in the WeChat group at the initial time of propagation is not a key factor affecting the knowledge transmission in the WeChat group. Therefore, managers do not have to blindly introduce knowledge owners from other companies to promote the knowledge transmission in the WeChat group by increasing the number of knowledge owners.