In this study, breakwater model which has several outlet pipes to discharge water is settled in the experimental open channel and mean velocity distributions of multi wall jet are measured. The length of flow of flow establishment of wall jet is shorter than that of free jet and decay rate of jet centerline longitudinal velocity along x is linear in 0.3 $leq$ x/$l_q$ $leq$ 17. The rate of vertical width and lateral width spreading of multi wall jet is respectively 0.0753, 0.157~0.190.