Based on the slope project of Zhangbei?Shangyi Expressway, indoor tests were conducted to obtain the mechanical parameters of rock and soil layers, variation law of shear strength of expansive soil with different number of cycles in dry-wet-freeze-thaw conditions was studied, and variation characteristics of mechanical parameters were revealed to deeply analyze the stability of expressway cutting slope excavation in the condition of expansive soil in overlying rock layers in alpine regions. By adopting MIDAS/GTS (SRM) software, the original slope excavation and support scheme of increasing the flattened down slope were simulated, and the improvement scheme of reducing the load by eliminating the cubic meter and installing anti-slide piles was put forward, with the stability compared and analyzed. The results show that increasing the cycle number decreases the cohesion and angle of internal friction of expansive soil, with the first cycle having the most prominent reduction effect. Additionally, the cohesion and angle of internal friction are no longer sensitive after five cycles. The dry-wet-freeze-thaw and freeze-thaw effects have the greatest influence on the degradation of cohesion and the angle of internal friction, respectively. Under the overlying rock layers of expansive soil in alpine regions, the excavation unloading, degradation of expansive soil layers in contact with water, and freeze-thaw-dry-wet-coupling effect are the main factors resulting in the reduction of mechanical parameters of soil layers, prominent deformation of side slopes, and side slide collapse. Compared with the measures of slowing down the side slopes and reducing the load by eliminating the cubic meter, anti-slide piles show the most significant effect on controlling the side slope displacement.