Aiming at real-time tracking of driving behaviors and improving safety, the paper analyzes and discusses the necessity, characteristics, architecture and function of onboard image-based on driving safety monitoring system. Directed against image collection, processing and understanding, based on digital signals processing technique, the paper also puts forward hardware design of onboard image-based on driving safety monitoring system, in which TMS320DM642, a kind of embedded DSP chips is used as a central processing unit. Software flow is also designed according to the driving traits. Experimental results prove that the system works well.