A multi-pair two-way amplify-and-forward relaying system is considered in this paper, where the K-pair users exchange information within pairs, with the help of a shared relay station. Each user is equipped with a single antenna while the relay station is equipped with a very large number of antennas N, where N≫2K. The impact of imperfect channel state information (CSI) due to the channel estimation errors on spectral efficiency (SE) and energy efficiency (EE) is investigated. Asymptotic expressions for EE and SE are obtained in this paper for three power-scaling schemes when maximum-ratio combining/maximum-ratio transmission (MRC/MRT) is adopted. Our analytical results reveal that when the number of relay station antennas N→∞, the effect of the small-scale fading can be averaged out; the residual self-interference and additional noise generated by channel estimation errors will completely vanish, and the inter-pair interference will disappear. However, the imperfect CSI deteriorates EE and SE. When there are no estimation errors, our analytical results reduce to the existing results. Simulation results confirm the validity of our analysis.