The plume dynamic characteristics from underwater pipe downward leakage are experimentally and theoretically investigated. The Lagrangian integral method is used to establish the dynamic model of downward plume. The model is numerically solved and the main plume parameters are obtained. The simulated results show that the simulated values in plume radius and length are generally consistent with the experimental values

but the simulated radius is higher than experiment value in area near plume terminal. The experimental and simulated results also show that for downward leakage the initial momentum of plume quickly decays and the plume length is very short compared with upward leakage. With increasing Froude number

the maximum length of upward plume rapidly grows while the maximum length of downward plume slowly grows.