The aim of steam trap control in SAGD process is to maintain certain steam-liquid level above producer, prevent steam breakthrough into the lower producer and improve heat energy efficiency. Nevertheless, it is almost impossible to monitor this liquid level, but to indirectly estimate steam-liquid level through monitoring subcool temperature difference between horizontal injector and producer. In order to accurately predict the height of steam-liquid level, a 2-dimensional steady state mathematical model reflecting the relationship of steam-liquid level, subcool temperature difference, pressure difference and liquid production rate was established, based on the assumption of simplification the shape of liquid pool into sector, which can be gained from earlier SAGD experiment conducted by Butler. Then, the theoretical model was confirmed a reasonably good approximation of steam-liquid level prediction by numerical simulation. Moreover, the moving law for steam-liquid level was analyzed under certain conditions of purified gravity drainage or certain pressure difference. Combined with dynamic monitoring and production performance data, this model can provide technicians_San important tool for predicting steam-liquid level location quickly and accurately.