Abstract: To evaluate the stability of the soil-rock mixture slope along the mountain road, and take corresponding protective measures, on the basis of summarizing the existing domestic and international slope research results and field investigations, according to the characteristics of the soil-rock mixture slope of mountainous roads, a first-level index (hydrometeorology, slope condition, rock and soil body) and 12 secondary indicators (rainfall, seepage, groundwater level; slope slope, slope height, slope morphology; lithology, lithology ratio, block gradation; vegetation type, root development state, and vegetation coverage rate) affecting the stability of earth and rock slope were selected. The evaluation system of the stability of soil-rock mixture slopes in mountainous roads was established. To deal with quantitative indicators and qualitative indicators, the standard of evaluation indicators was set up, and the 15 actual slope data were discarded. The evaluation index and stability level of the slope were divided into four levels, and the corresponding level range was given. The weight value of each evaluation index was determined by the rough set theory. Finally, based on the theory of extenics, the extension stability evaluation model of soil-rock mixture slope in mountainous area was established, and the stability of the slope was evaluated. The model was applied to verify the slope in the S314 section of the provincial highway. The evaluation results show that the evaluation model is scientific, reasonable and reliable, which provides a new reference for the practical application of the project.