Abstract: In view of optimization of treatment of slopes with interbreeding of soft and hard rocks,there are problems of scheme preference and objectiveinformation.And based on cosine decision principle,the cosine decision method has been established for optimization of slopes treatment scheme with interbreeding of soft and hard rocks.First of all,this method divides the evaluation index into 5 levels,and the weight of index is determined according to its level.And then according to the cosine formula,calculated the cosine of the angle between the index line of evaluation scheme and ideal target line segment,and building a model of optimization of treatment of slopes with interbreeding of soft and hard rocks.The model is applied to the optimization of Pengjiawan slope control scheme and the optimal treatment scheme is obtained,thus it provides the basis for its treactment design and construction decisions.