Experiments demonstrated that the weeping. is mal-distributed and occurs mainly in a region of tray deck next to the inlet weir. The amount of weeping in this region depends on the weeping rate. On this basis, three types of weeping. distribution are proposed. The effect of mal-distributed weeping on the Murphree tray efficiency is evaluated by using the three-dimensional non-equilibrium mixing pool model, where the influences of the flow pattern and the variation of Murphree point efficiency on a tray are taken into account. The calculated results reveal that the extent of Murphree tray efficiency drop depends chiefly on the degree of mal-distribution and the percentage of. weeping. It is also demonstrated that in the determination of the lowest operating limit of vapor velocity, the unfavorable effect of mal-distributed weeping should be considered as an important factor and cannot be ignored.