Steel slag (SS) and rice husk ash (RHA) are utilized to treat high plasticity clay (CH) for highway subbase applications. The aim of this paper is to study the curing effect of SS and RHA addition on treated CH and explore the stabilization mechanism. The paper systematically investigated the mechanical properties of stabilized soil, such as California bearing ratio (CBR) and unconfined compressive strength (UCS). In addition, the micro-improvement mechanisms of the soil properties were explored through X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and atomic force microscopy. The results showed that the mechanical properties of solidified soil were significantly improved after adding SS-RHA. With the addition of 15 % SS and 9 % RHA in CH, the CBR, UCS, and elastic modulus were increased by 412.5 %, 384.1 %, and 374.7 %, respectively. The addition of SS provided the calcium and aluminum ions required for the hydration reaction. Meanwhile, the pozzolanic activity of RHA can enhance the activity of SS and further improve the gelling property of SS. The microscopic characteristic tests showed more cementitious material was generated in the SS-RHA stabilized soil, which were more uniform and denser. The stabilization mechanism was attributed to the internal pore filling and interparticle cementation of SS-RHA gel, which simultaneously enhanced the microstructure of the soil and particle contact.