Ecological compensation is a new resource and environment management model. As one of the main areas for implementing ecological compensation policies, basin ecological compensation has become an important measure for encouraging basin pollution control projects and improving the quality of regional economic development. By applying the basic game analysis of evolutionary game theory and building an evolutionary game model with a “reward–punishment” mechanism, this paper compares the interest-related decision-making behaviors of the upstream and downstream stakeholders of basin ecological compensation. By using data on the water quality of Xiangjiang River Basin, this paper calculates the rewards and penalties in different intervals by building a parametric regression mathematical model and employing the local linear regression method. Results show that a decline in water quality should be fined RMB 925500 yuan, an improvement in water quality should be awarded RMB 1227800 yuan, and a deteriorating water quality should be severely fined RMB 5087600 yuan.