Abstract: Digital economy is an important direction for China's future development, and the peer effect plays a very important driving role in the development of digital economy. Based on the data of the“Singles'Day”Online consumption survey in 2019, the theoretical and empirical studies based on the imperfect information Bayesian decision model show that the peer effect can have a significant impact on the herd behavior of consumers, and this impact will increase at a decreasing rate with the increase of the number of peers. Further data analysis shows that due to the network information externality and payment externality, each additional partner participating in the“Singles' Day”activity will, on average, increase the probability of consumers participating in the“Singles' Day”activity by more than 8%. After the treatment by using the instrumental variable method and the propensity index matching analysis, the result remains significantly valid. This shows that there is a certain degree of irrational exuberance in the development of the digital economy. To maintain the healthy, sustainable and stable development of the digital economy, it is necessary to optimize and improve government policies, business management and individual decision-making.

Key words: peer effect, herd behavior, Bayesian model, network externality