This paper studies the coordinated multicell downlink transmission to cope with the severe inter-cell interference (ICI) in future cellular systems. We propose an iterative scheme to jointly optimize the base station (BS) and relay beamforming weights to maximize the worst-case signal-to-interference-and-noise ratio (SINR) with perfect channel state information (CSI), under two different types of BS and relay power constraints, respectively, which are the total power constraints and individual power constraints. Using the semidefinite relaxation (SDR) technology, the optimization problems for BS and relay beamforming weights can be converted into semidefinite programming (SDP) problems, which can be effectively solved by interior-point methods. Simulation results demonstrate that the proposed iterative scheme can achieve near-optimal performance within a few iterations and provide a good tradeoff between performance and cost (i.e. the number of BS antennas and relays) in the multicell systems.