Abstract: Understanding the primary and secondary relations of influencing factors is crucial for predicting deformation and controlling collapse in cutting slopes. Using a cutting slope along the Shuangcheng−Dalijia expressway in Gansu Province as the research object, this research utilized the FLAC^3D finite element software platform to establish dynamic correlations between saturation, gravity, and soil shear strength through FISH language. Based on this, safety factors of the cutting slope were calculated under different rainfall intensities, slope ratios, and rainfall duration. Grey relational theory was applied to determine the primary and secondary relationships of key factors affecting shallow collapse of cutting slopes under rainfall conditions. Indoor rainfall experiments and on-site ecological protection tests were conducted to summarize the shallow collapse mechanism and propose the environmental control measures. The study revealed that the failure mode of cutting slopes transitioned from deep overall sliding to shallow local sliding during rainfall. As the slope ratio decreased, the shallow collapse area gradually shifted from the slope shoulder to the foot of the cutting slope. Cumulative erosion rates of shallow soil in cutting slopes decreased initially and then increased over time during rainfall. Installing arch skeletons and reducing the slope ratio enhanced the cutting slope's resistance against shallow collapses. Among with the protective materials, polypropylene fiber-reinforced soil protective materials exhibited the best timeliness and ecological control effect for shallow collapses of cutting slopes compared to HP-FGM and EFM materials.