It is vital to implement multicast congestion control in networks as multicast improves the link's transmission efficiency, but it is apt to cause network congestion. However, multicast congestion control designed for Internet isn't fit for Ad Hoc networks, due to the following features: (1) multi-hop wireless-based transmission resulting in the contention relationship between flows in both the time domain and the spatial domain; (2) and frequent node mobility leading to the time-varying network situations. In this paper, the notion of the link's interference set is introduced to describe the characteristics of the contention relationship between flows, and a nonlinear optimization problem is presented to formulate the multirate multicast congestion control problem for small time interval where network situations can be regarded as time-invarying. The penalty function method and the subgradient method are jointly applied to obtain the optimal solution, and thus the distributed iterative algorithm is proposed. On the basis of this distributed algorithm, an adaptive congestion control strategy for multirate multicast sessions (AC²M²) is proposed to cope with the time-varying network situations, by means of network status detection and receding optimization. Simulation results show that the proposed distributed algorithm can quickly converge to globally optimal solutions; and, compared to the AIMD algorithm in TCP-Reno, AC²M² is more adaptive to time-varying network situations, and achieves better network performance.