In vehicular ad hoc networks, network coding and cooperative for message propagation have attracted considerable attention as ways to reduce the outage probability to improve the system performances. In this paper, we analyze the exact expression of outage probability and give an approximated expression over the Nakagami-m fading channel with dynamic network coding(DNC) and MIMO dynamic networks coding(MIMO-DNC). Simulation results indicate that the approximated curves are matched well with the exact ones at high SNR. Compared with the exact expression, the calculation amount can be reduced by the approximated expression.