Taking as an example, the flat base condition work of an affordable housing project of a university in Chongqing, this paper introduces the application of civil 3d in accurate calculation of earthwork quantity, particularly how to create curve design in complex situations and how to do slope-excavation. As a result, the 3D effect drawings of the Flat-Earth Work and dig-fill quantities of the Earth Work, supply party A and party B with theoretical foundation for computing project′s outlay.