In a long historical period, the social network based on kinship and neighborhood played an important role in the rural society of China. China's rural revitalization policy has brought rural development into a new era. In this research, we have explored whether the characteristics of the traditional rural social network have changed in the current period, and whether and how the social network, as an informal system, affects peasant households' land use decisions. We used social network analysis to portray the characteristics of peasant households' social network and adopted network autocorrelation analysis to test whether the social network affects peasant households' land use decision-making, and finally employed regression models to revel the mechanism among the social network, livelihoods, and peasant households' land use decision-making. Our research results showed that the social network of peasant households based on kinship and neighborhood was featured by subgroups and small-world phenomenon, indicating that the pattern of traditional rural social relationships has not changed. Besides, our results also revealed that the social network influences peasant households' land use decision-making by making it more similar, that is, the decision-making presented peer effects. In peer effects, the influence of the neighborhood network was greater than that of the kinship network, and when the social relationship reached the fourth-order, peer effects would no longer exist. Furthermore, the social network can not only regulate the simplification and food-crop preference of planting structure caused by livelihood changes but also directly reduces the food crop proportion and increases land investment intensity. Our research results emphasize the importance of using peasant households' social networks to guide land use in the process of rural revitalization to better implement agricultural policies.