In order to analyze the influencing factors for stability evaluation of highway slope， assessing the stability grade. Based on the AHP method and extension set theory，the assessment model of slope stability was established using extension hierarchy method. The multi-level assessment index system was established，the weight order of assessment indices and the comprehensive correlation degree of each level index were calculated. The construction stability of a rock cutting high slope in the Guanglian highway subgrade was evaluated using the model. The research results show that the comprehensive correlation degree of the slope stability is -0.447 9，-0.188 0，-0.013 1，-0.014 3， -0.339 8，respectively. The grade characteristic value of the stability evaluation is 3.3154，and the evaluation result is grade Ⅲ to grade Ⅳ ，which is consistent with result from the field survey. The model can provide reference for stability evaluation of highway slope and construction plan.