Aiming at the problem of limited power consumption and battery capacity in unmanned aerial vehicle(UAV)-assisted multi-user multiple input multiple output (MU-MIMO) emergency communication networks, a method is proposed for power-constrained conditions. The design of beamforming to maximize the total transmission rate of the system is optimized. First, a method for easy determination of UAV position without iteration is proposed. Second, considering that the problem is non-convex, the first-order Taylor approximation is used to approximate it convexly. The second-order cone programming (SOCP) reduces the computational complexity and solves the best beamforming vector. The simulation results show that the proposed method is suitable for multi-user communication systems. Although the interference cannot be reset to zero during the simulation process, the system's total transmission rate can be maximized by suppressing the interference.