V2V transmission of Safety Warning Message (SWM) can provide warning before emergency occurs to avoid accident, and remind surrounding vehicles to avoid potential danger. There are two main problems that will affect the transmission performance of SWM, namely the high local flow and low efficiency caused by high probability of sub-health vehicles (SHV) and traditional single channel and flooding transmission mechanism. Therefore a novel channel allocation algorithm based on communication demand matrix has been proposed in this paper. A new parameter, communication demand relationship based on health evaluation results is defined and communication demand matrix (CDM) is constructed to measure the transmission demand between corresponding vehicles. Then intra-cluster channel allocation algorithm based on the CDM is studied to effectively allocate the channel resource and improve SWM dissemination performance. The simulation and experimental results show that the proposed mechanism has much higher ratio of fulfilled communication demand in the same time slots than flooding based on communication demand relationship (FD) methods in low, medium, and high vehicle density scenario. Beyond that, the proposed mechanism has better performance in receiving messages than FD and flooding.