Abstract: Neogene hard clay is widely distributed in the Cenozoic basins of east China, and is the main subject of regional studies of special sedimentary materials for its special properties. The middle line of the North-South Diversion Water Project lies across the west edge of Nanyang basin and the north China basin, excavating in various kinds of Neogene hard clay. Based on laboratory experiment and measurements, this paper presents the engineering geological properties of Neogene hard clay from the Nanyang basin, as well as Fangcheng Baofeng and Handan Yongnian regions, including the composition and physicochemical properties, physical properties shrink-swell characteristics, strength and other properties, and summarizes their formation mechanisms and variation laws. Meanwhile, the environmental effect under different humidity and lateral pressures is summarized, which is helpful to understand the deformation mechanism of Neogene hard clay under the condition of excavation and engineering operation.