The Internet of Vehicles (IoV) has attracted increasing attentions for its potential of enhancing driving safety and traffic efficiency. The Multi-hop broadcast is one of the important techniques for time-sensitive data dissemination especially in emergent cases. As a result, how to wisely select the next-hop during Multi-hop routing plays an important role for performance improvement in IoV as well as dependent applications. Nevertheless, in view of the high mobility, frequent changing topology and complicated channel environment, a hazardous and thoughtless selection of the next-hop is easy to make, thus leading undesirable results. To deal with this issue, in this paper, a probabilistic broadcasting protocol for emergent message dissemination (BP-EMD) in Urban IoV is proposed. As the selection guidance for relaying node, the weighted probability is envisioned for each potential relay candidate, which is the combination of distance, link availability and packet reception ratio. After that, the node with the greatest weighted probability has been given the highest priority to relay the packet. In case that the selected relay node fails the forwarding, the other nodes available for relay will assist to disseminate the packet. In this way, the transmission reliability of the emergent messages is significantly guaranteed. Numerical results indicate that our BP-EMD can achieve higher broadcasting efficiency and less redundancy with less delivery latency, average transmission numbers and average End-to-End delay, as well as high packets delivery ratio and dissemination efficiency, compared with some classical multi-hop broadcasting protocols.