Broadcast is one of the most important communication means in mobile ad hoc networks. Reactive routing protocols establish routes by broadcast. Conventional on-demand routing protocols suffer in terms of several issues such as rebroadcast redundancy and collisions. This paper proposes an algorithm called DBA(Density Based Algorithm) .DBA calculates sending delay and forwarding probability based on neighbors of nodes and adjusts them dynamically according to the broadcasting situation. The strategy of extending cache is adopted to solve the problem of network division. Combining with the classic AODV routing protocol, we design the AODV-DBA protocol. Computer simulation results confirm that AODV-DBA performs perfect in terms of redundancy and collisions compared with the other protocols, and the DBA algorithm could effectively reduce the cost of channel resource occupied