The selection of the design plans for deep cutting slope of high-level highway in mountain area,in general speaking,only depends on the designer's experience and intuitive determination at the present time,which results in unreasonable,even error,decision or plan.It unavoidably causes enormous damage.This paper proposes to adopt correlation degree analysis method of grey system theory for choosing the optimal design plan.It will give a definite and real meaning about choosing design plan and avoiding or reducing errors in design work.