The scientific evaluation research about smart city has a great influence on its development，and it can be explained from three perspectives “Front，Middle，and Back”. “Front” means that the evaluation framework and index can provide the city which prepares to build smart city with a forward-looking guidance about development target and project layout. “Middle” demonstrates that the evaluation framework and index can facilitate decision makers to adjust projects in time，correct errors and play an important role in standard optimization for the city which is building smart city. Last but not least，“Back” implies that it can scientifically measure the level of smart city，learn from the best cases and lessons，optimize the construction projects and easily improve by making good use of the results for the city which has achieved a certain effect of the smart city construction.