Abstract: Through a dynamic analysis of transverse vibration of a log truck with trailers, the author put forward a theoretical formula on transverse vibration of the truck. Every roof of the characteristic equation made from the vibration system indicates a movement with a formula of φ=A_ie^λt, which provides a possibility for us to seek for the dynamic stability. From the factors studied in this paper, the author concludes that any form movement is relevent to the structural dimension of the truck, such as the length of the trailer, the length of the pulling rod, the wheelbase, the location Of the centre of gravity, etc. The best structural dimension of the trucks can be found out based upon the dynamic theories.