Abstract: The projection plane transforming method can change the spatial geometric element’s
position relative to the plane of projection in the descriptive geometry and the new projection is more
conductive to solving problems. In the statics, the vector force can show in a straight line, the
equilibrium problem of spatial arbitrary force system can turn into the diagram and legend among the
line, this paper tries to combine the strengthen of projection plane transforming method into solving of
the equilibrium problem of spatial arbitrary force system in a direct way. Using CAD as a drawing tool
can ensure the mapping precision and speed, which is a practical and effective method to solve the
spatial arbitrary force system.

Key words: projection plane transforming, CAD, spatial arbitrary force system, equilibrium of forces