The AS-level Internet topology has shown significant clustering features. In this paper, we propose a new set of clustering metrics and conduct extensive measurement on the AS-level Internet topology. We give a thorough characterization on the clustering features and their evolution. We also study the clustering features of different topological structures by comparing the Internet with various topology models. Due to the limitation of existing topology models on capturing clustering features, we design a new topology model based on clustering. Through extensive evaluations, we claim that our model can closely capture the clustering features as well as other common topological properties.