The constraint-oriented layout design problem is one of the hot spot in the research of layout field．This paper presents a layout generatmn algorithm based on geo-metric reasoning．Using the advantage of the parametric design，the algorithm sets up the relations between the parameters which determine the result of the layout design, also it has several advantages in flexibility，expansibility．1ocal modification of the main parame- ter which is able to check the consistency of the constraints．The algorithm has been SUC-eessfully applied to the cab interior layout design system.