Ganjiang River, the biggest river in the largest freshwater lake in China, Poyang Lake, provides ecosystem services for approximately 20 million residents in the basin. This study, focusing on the value of ecosystem services and willingness to pay (WTP), can be applied to both establishing and enforcing a compensation mechanism for watershed ecology. The study, using the Tobit model within the framework of random utility theory and actual data from a survey, analyzed the residents' WTP for ecosystem services and its influencing factors. In addition, it estimated the value of ecosystem services using the contingent value method. The highlights are as follows:Firstly, microscopic factors, including psychic distance and psychological ownership, were incorporated into the residents' WTP model. The study also analyzed how to increase the value of ecosystem services via calculating the partial effect of psychological factors in WTP. Secondly, considering the differences in ecological, economic, and social conditions among the upper, middle, and lower reaches of the basin, the heterogeneity of different regions was considered in the evaluation of the residents' WTP. The results showed that:(1) Besides the factors of residents' income and age, the main influencing factors included the satisfaction of environmental management, payment preference, degree of trust in the local environmental protection department, psychic distance to the river, and ownership of it. (2) Regional heterogeneities of residents' WTP were caused by payment preference, degree of trust in the local environmental protection department, and residents' income. (3) The partial effects of satisfaction, trust level, psychic distance, and psychological ownership were 7.22, 3.84, 2.78, and 1.85 Yuan per month per household, respectively. (4) The median WTP in Ganjiang Basin was 19.57 Yuan per month per household, and the WTP for ecosystem services in Nanchang, Ji'an, and Ganzhou were 23.24, 19.70, and 16.86 Yuan per month per household, respectively. In addition, the value of ecosystem services of Ganjiang River was estimated at over 1.36 billion Yuan per year, and those of Nanchang, Ji'an, and Ganzhou were 0.431 billion, 0.321 billion, and 0.465 billion Yuan per year, respectively. Finally, corresponding policy recommendations were proposed based on the findings of this study.