The United Habitation in Marseilles is the master wok of Le Corbusier, the well-know architect. Over the fifty years of its existence, the researches concentrate on its light and shadows and color scheme of the facades, etc. However, the most important original intent of the designer is the optimization of the indoor thermal environment, especially the use of cross ventilation. As green building has drawn more and more attention nowadays, this article will focus on the indoor natural ventilation conditions of two standard cells of the Marseilles Unit, which are known as the ‘upper E’ apartment and the ‘lower E’ apartment, by using computational fluid dynamics (CFD) models. Compared with the data of Middle corridor type dwelling, verify the superiority of its architectural layout.