UAV aided wireless communication has the advantages of flexible deployment and large coverage, but it still has the disadvantages of large path loss, low throughput and transmission capacity. Beamforming technology is introduced into UAV aided wireless communication, which can effectively compensate the communication path loss and mitigate intra cell or inter cell interference. Therefore, this paper constructs a UAV aided wireless communication system model, which is equipped with a uniform plane array on the ground base station and UAV to achieve beamforming, so as to maximize the system capacity. For the nonconvex problem with high dimensional and highly coupled optimization variables, an efficient iterative algorithm is proposed to jointly optimize the position of the relay UAV and beamforming vector. Firstly, the original problem is transformed into two subproblems of the position optimization of the relay UAV and beamforming vector optimization by the block coordinate descent method, and then the two subproblems are transformed into a convex optimization problem by the successive convex approximation algorithm. Experimental results show that the proposed optimization theory and algorithm have good convergence performance and can effectively improve system capacity.