The subject of this study concerns Urmia Lake which is one of the most valuable water habitats in Iran and investigation of crisis in the drop n of water level, significant decrease in the lake’s surface area and increase in its salinity.. In order to have better understanding of the processes that affect the lake's water level fluctuations and assess the contributions of every responsible parameter, System water consumption was designed. System water consumption was designed in The Lake Basin in the Vensim and the effects of each variable on the water level of the lake were evaluated using a set of different scenarios The findings suggest that in comparison to other variables, the operation of dams (26%) as well as an increase of water requirement (16%) by variables have played a role in reducing the input to the lake. Climate variables had an effect of 16% within the time span of 1999-2014. Although Hydrograph indicates the aquifer deterioration in some of them, the entrance to the lake water budget is negligible