Abstract
A qualitative reasoning approach is used for the spatial configuration of mechanisms in conceptual design phase. The appropriate types of mechanisms are chosen firstly for a specific reasoning task. The qualitative vectors of the basic components are given to construct the compli-cated mechanism. Based on the qualitative sign algebra rules, the reasoning algorithm is presented to reason the spatial configuration of the selected mechanism. The static reasoning process of the mechanism structure in-side a truck is shown finally, which indicates that the qualitative reasoning can be an assistant method when the numeric information is incomplete.