In view of the different goals and demands for the smart grid in different periods of time， its dynamic assessment method based on system dynamics is proposed that takes the smart grid investment as the starting point in developing a system dynamics model， which reflects the dynamic relationship between smart grid construction results and intelligent techniques realized through investment. In addition， the model quantitatively analyzes the causal feedback relation between the two and gives the smart grid effect indices in the evolution of the trend over time. The evaluation model is proved effective and rational by simulation results.