Abstract: The principal purpose of the present work is to investigate the effects of hydrochemistry on the structural strength of Zhanjiang formation clay. Several hydrogeological data and chemical composition of groundwater by drilling are collected and analyzed to evaluate the chemical environment of groundwater in Zhanjiang area. The water solution in soils is extracted by using the centrifugal filter method to measure its chemical composition. Furthermore, changes of microstructure before and after removing the cementing material are studied using the scanning electron microscopy and energy spectrum analysis. The results show that the water solution in Zhanjiang formation clay has chemical compositions and relative content similar to the groundwater with the chemical types of Cl-Na, showing acidic and iron-rich characteristics. The high content of iron can provide cementing materials, and free iron oxides further produce a strong bond between soil particles in the acidic environment. According to the results, an effect mechanism of hydrochemistry on the structural strength of Zhanjiang formation clay is proposed. The strong structural characteristic is caused by an open flocculation structure and the bond between the particles.