Farmland water conservancy governance is important for food security and the stability of rural societies. Based on the questionnaire survey data of farmers in the well-irrigated area of Hebei Province, this study evaluated the impact of small farmland water conservancy selfgovernance on governance performance through the ordered Probit model, and used the threshold effect model to obtain the threshold value of the user scale and analyzed the moderating effect of land fragmentation on small farmland water conservancy governance performance. The research found that: (1) The self-governance mode of small farmland water conservancy in the studied wellirrigated area resulted in poor facility maintenance level. There is no significant difference in water disputes among farmers under different governance methods. (2) In the influence of selfgovernance on the maintenance level of facilities, the scale of users has a threshold effect. The threshold for the number of water-using farmers in the study area is nine households; when the number of water-using farming households is higher than the threshold, self-governance leads to poor facility maintenance. (3) Land fragmentation has a moderating effect on self-governance performance. The higher degree of land fragmentation, the worse governance performance of selfgovernance mode in facility maintenance. Based on the above results, it is recommended that village grassroots organizations should be the main body of responsibility, and there is a need to improve the self-governance mode of small farmland water conservancy in well-irrigated areas by formulating unified maintenance measures and a progressive reward and punishment system. By guiding cooperative operation, optimizing the distribution of motor-driven wells, and reducing the degree of land fragmentation, the government can help to achieve a reasonable scale of irrigation and effective and autonomous governance of water conservancy in small-holder farmland areas.