This paper analyzes the system-level performance of the long term evolution (LTE)/LTE-Advanced (LTE-A). LTE/LTE-A has been considered to be a promising next generation communication system. It is proposed to ITU-R to be acknowledged as an IMT-Advanced technology. The performance of candidate technology proposals for IMT-Advanced should be evaluated to see if it satisfies the predefined minimum requirement of ITU-R. Note that ITU-R provides a report on evaluation guidelines, assumptions and minimum requirements, and it is strongly recommended that the guidelines and assumptions are followed when evaluating performance. This article summarizes the simulation methodology based on ITU-R guidelines and investigates the key technology, Multi-User MIMO (MU-MIMO), of LTE/LTE-A for IMT-Advanced. Simulation shows that LTE/LTEA with the advanced MU-MIMO feature achieves performance above the ITU-R requirements, which cannot be achieved with Single-User MIMO (SU-MIMO).