In this paper, we propose a post-layout waveform prediction method by System Identification (SI) based on the fact that the waveforms of pre-layout and post-layout are always correlated. Mathematical models are built to describe the relationships between the pre-layout and post-layout simulation results via SI techniques. The model parameters are calibrated by using the simulation results of the first few data points of pre-layout and post-layout stages. By taking the corresponding pre-layout simulation results as inputs of the calibrated models, the rest post-layout waveforms can thus be predicted as the output of the models. Several examples demonstrate the efficiency of the prediction, which helps the designers have a quick view of the post-layout waveforms in the design process.