Abstract: The third-party management of agricultural waste is an important way to alleviate non-point source pollution and improve the recycling rate of resources. Its stable operation depends on the continuous participation of agricultural producers and third-party management enterprises. Being vulnerable to seasonal alternation is a remarkable feature of agricultural production. The evolutionary game model of third-party management under the alternation of seasons was constructed, and the strategy choice of both sides was analyzed. Case studies of two centralized agricultural waste management projects of Jiangxi Zhenghe Environmental Protection Engineering Co., Ltd. were done. The research shows that the stability of third-party management is affected by seasonal alternation, and there are two periodic variation laws. But the specific change law depends on the relationship between the cost of legal treatment of waste and the cost of illegal treatment of waste; the cost of illegal treatment by the agricultural producers should be increased. The stability can be effectively improved by increasing the cost of illegal treatment by agricultural producers, reducing the participation cost of both parties. It is suggested that the government should formulate targeted short-term policies and combine them with long-term policies according to the periodic variation laws, and use the combined policies to promote the long-term stable operation of third-party management of agricultural wastes.