In order to ensure the precision of safety data in VANET, the safety-related data often requires a higher priority and preferred dissemination, which the existing data dissemination algorithms of VANET cannot satisfy. In order to meet the demand of the differentiated transmission priorities of safety data in VANET, we propose a model of data priority and an algorithm of safety data dissemination based on data priority and vehicle density, called priority density transmit (PDT). Firstly, in order to differentiate the data priority of different packets, we propose a model of data priority, which assigns different priorities based on data state. Secondly, based on the difference of data priority and vehicle density, we propose an algorithm of safety data dissemination—PDT, which dynamically assigns the counter threshold and collision window based on data priority and vehicle density. Dynamically assigning the collision window can ensure the transmission order of data, and dynamically assigning the counter threshold cannot only ensure reliable transmission of data but also reduce the broadcast storm. We evaluate the performance of the PDT by comparing it with the counter-based algorithm and slotted-P algorithm. Simulation results show that the PDT can significantly improve vehicle throughput and packet delay, and reduce the broadcast storm.