Abstract: Land acquisition and resettlement management of major water conservancy and hydropower projects is a systematic endeavor that affects project construction progress, regional social stability, and economic development, and is characterized by complexity. Based on management experiences from land acquisition and resettlement in mega water conservancy and hydropower projects in Hainan Province, this study adopts the grounded theory approach to identify eight influencing factors across three complexity dimensions: object complexity, organizational complexity, and process complexity. These factors include the complexity of land ownership relationships, the complexity of specialized project handling, the complexity of land acquisition and resettlement compensation, the diversity of participating entities, diversified interest demands, deviations in role understanding, environmental uncertainty, and the dynamic balance of multiple objectives. Subsequently, a Fuzzy Cognitive Map (FCM) model is constructed for evolutionary analysis. The results show that all these influencing factors significantly affect the complexity of land acquisition and resettlement management, among which diversified interest demands, the dynamic balance of multiple objectives, and the diversity of participating entities are the most influential ones. Based on the results of FCM predictive analysis, diagnostic analysis, and sensitivity analysis, coping strategies are proposed, including establishing effective communication mechanisms, multi-dimensional demand collection mechanisms, differentiated negotiation mechanisms, and graded early warning mechanisms. The research findings help deepen the understanding on complexity of land acquisition and resettlement management in mega water conservancy and hydropower projects and provide practical suggestions for such management.