Abstract: Salt water intrusion in estuaries, which occurs naturally and affects the quality of water for various uses, is an urgent environmental issue. The Qiantang Estuary, as the main source of freshwater supply to Hangzhou city, is experiencing serious salt water intrusion in recent years. Although 2D and 3D numerical models are common tools for prediction of salinity intrusion at present, analytical models of salinity variations require smaller data sets and hence are much more efficient. In this paper, a predictive salt water intrusion model is developed for prediction of both high water slack and low water slack in this typical macro-tidal estuary with topography well described by an exponential function, based on Savenije’s one-dimensional steady equation. This model was calibrated and validated against field data of water flow and salinity collected on 7-9 November (neap tide) and 14-16 November 2012 (spring tide), and its salinity predictions agreed well with measurements. The salt intrusion length estimated using the model also achieved a satisfactory accuracy.