Underlying principles and content of new technology for automated hydrological predictions of poorly gauged and ungauged basins were reviewed herein. Basins classification principles depending on availability and spatial-temporal discreteness of observations of meteorological and hydrological variables were proposed. The prediction procedure for large river systems insufficiently covered by hydrometeorological survey was outlined. Prediction methodology for Sông Sê San river basin, which is the left tributary of Mekong river, was tested. Possible options for preliminary calibration and validation of MLCM3 predictive model (Multi-Layer Conceptual Model, 3rd generation), developed within the framework of set task, were described. The software, implementing the streamflow prediction method for ungauged and poorly gauged special basins of large rivers tributaries, was tested.