Vehicle ad-hoc network (VANET), as an application of mobile ad-hoc network and sensor network on road, has no an integrated protocol architecture, and has no special transmission control protocols available. In order to provide the reference for transmission protocol design of VANET, this paper investigates the goals and elements that the transmission protocol design should conform with. At first, this paper introduces the characteristics and applications of VANET, and the challenges of transmission control of VANET. Then the classification standards for wireless transmission protocol are presented. The advantages and disadvantages are discussed with analysis and comparison if various classes of wireless transmission control protocol are applied to VANET. Furthermore, according to the characteristics of VANET, the goals and elements of transmission control design of VANET are proposed. Finally, the research trends of transmission control of VANET are prospected.