Abstract: In this paper, we consider an OFDM-based amplify-and-forward (AF) relay system in the presence of multiple co-channel interferences (CCIs). On the premise of severe CCIs in both the data and pilot subcarriers, we propose an iterative approach for the pilot-aided channel estimation and derive the CramerRao Bound (CRB) of the channel estimation. The estimation values of all channel state information (CSI) and the equivalent noise covariance are combined linearly at the receiver to mitigate the degradation which comes from the CCIs, so the detection performance of the receiver can be improved effectively. Simulation results show that when multiple CCIs exist in the OFDM-based AF relay system, our proposed channel estimation method can effectively estimate all CSI of the equivalent channel and the interference channels and the equivalent noise variance, and its mean square error (MSE) performance is as good as the traditional linear minimum mean square error (LMMSE) channel estimation, with the advantage of the lower complexity.