In vehicular ad hoc network (VANET), the efficient coverage and low transmission collision of safety message is the challenge. To solve this problem, a VANET broadcast mechanism based on probability and backoff (VBM-PB) are proposed in this paper. The mechanism is part of the recipient mechanism and is practicable due to low complexity and fully distributed computation. The geographical position and data load of vehicles are both considered to calculate the forward probability of each potential relay in VBM-PB. A function of forward probability is constructed combined with an adaptive backoff mechanism, which can reduce packet redundant in the network, relieve data collision among nodes and enhance coverage rate of safety message. Besides, timeout-retransmit mechanism is also applied to guarantee high reliability of transmission. The simulation results show that the performance of VBM-PB is superior to several traditional mechanism in terms of package permeability, forwarding node proportion and transmission delay.