In this letter, we consider the fifth-generation (5G) wireless backhaul network with small cells and millimeter-wave (mm-Wave) communication. We assume mm-Wave wireless backhaul is used for a physically separated 5G macro base station (MBS) to communicate with small-cell base stations (SBSs) that have wired connections to each other. Thus, a user in the coverage of the SBSs can receive its desired signal when at least one of the SBSs is connected to the 5G MBS. However, a blockage problem of line-of-sight paths can induce an outage event in mm-Wave communication. Using stochastic geometry and random shape theory, we analyze the outage probability of the mm-Wave wireless backhaul in the presence of blockage and investigate impacts of various system parameters.