Considering the problem that maximizing the sum rate of multi-user MIMO system,an algorithm that joints iterative interference alignment and allocation strategies of degrees of freedom(DoF) is proposed in this paper. DoF allocation of multi-user MIMO system is achieved via Tree Search algorithm. Theoretical analysis and simulation results show that the proposed Tree Search algorithm achieves sum rate performance near that of the exhausting search(EX)asymptotically, while the Tree Search algorithm has lower ...