Waste sorting management with third-party supervision is a new mode for many cities in developing countries. Based on the evolutionary game theory, this paper studies the evolutionary trends and equilibrium points of the tripartite game of waste sorting. The main research findings include: (1) the tripartite game has two possible evolutionary stability strategies; (2) the key condition for the three parties to take positive strategies is that the sum of their waste reduction reward and paying penalty is greater than their cost for waste sorting; (3) the decrease of one party’s cost, the increase of its reward and penalty, the rise of recycling price and the growth of recycling quantity can promote its choice of positive strategy; (4) one party’s variable changes do not only change its own strategy choice, but also adjust the strategy choice of the other two parties in the same direction; (5) the internal adjustment of waste reduction reward among three parties cannot help the three parties to choose the positive strategy. This paper is the first to study the third-party supervision issues of waste sorting using evolutionary game theory. The findings and strategy suggestions are helpful for waste sorting management.