The water consumption of Tianjin was forecasted by multiple linear regression model. Firstly, using the main composition analysis method, the independent variables were chosen as population, GDP, rate of industrial water reuse, the average rainfall and the green cover percentage. Then established the dependent program by the R language and made a Mathematical Model to do the muhiple linear regression. It can be seen that the purpose of the regression model is good through researching the validity of the residual analysis model. This article provides the reference for accurately forecasting the urban water consumption by a simple method.