The product assembly quality is influenced by the coupling effect of multiscale geometric errors. Acquiring the influence of dimension, tolerance and microtopography on part surface quality is the key factor of improving prediction accuracy of product assembly quality. Since the current technology of part solid modeling is difficult to represent tolerance information and surface topography information in computer aided design (CAD) model uniformly, and the accuracy of product assembly simulation and analysis is reduced, the realistic geometry based feature modeling of complex part and its application in assembly quality analysis are studied in this paper. First of all, the novel concept of realistic geometry is proposed, which integrates several geometric elements such as ideal geometry, variational geometry, and fractal geometry. Then, the hierarchical representation model of realistic geometric feature information of complex part is established, and the concrete method and steps to generate the realistic geometric solid features of complex part are proposed. Finally, the efficiency and feasibility of the proposed theory in this paper are validated by assembly quality analysis of the guide rail and sliding table of the machine tool.