Abstract: The wave input model (WIM) cannot express the non-uniform characteristics of ground motions completely. By analyzing the spatial evolution of seismic waves from the source to the site, the incident site waves are proved to be complex waves. A strategy for improving the WIM by expanding incident waves to complex waves is proposed. The new model is named the non-uniform wave input model (NUWIM). The NUWIM is accomplished by the deterministic incident site waves and the visco-elastic boundary and is verified by the analytical ground motion. The result shows that the advantages of WIM in simulating the wave propagation effect and the radiation damping effect are inherited in the NUWIM, which can effectively achieve the input of complex incident site waves. Compared with the WIM, the non-uniform characteristics of ground motions, such as time delays, peak variations, and time history shape differences, can be synthetically simulated by the NUWIM.