According to the experimental results of Au atomic aggregaties on molten glass surfaces with impurities, based on the characteristic assumption that clusters diffuse with random diffusion steps and rigid rotation angles, an improved restri cted cluster_cluster aggregation model for nonlattice substrates with impurities is established. Then the whole diffusion，rotation and aggregation processes of the clusters are simulated. The impurities are distributed on the nonlattice su bstrate ramdomly, and its influence on the properties of the ramified aggregates is studied systematically .The simulation data are in good agreement with the e xperimental results.