The invention discloses an NS3 simulation system traffic importing method based on Netflow. On the basis of lack of an NS3 simulation system traffic modeling method, a true traffic data importing function is added to a simulation system by employing the advantages that an NS3 is designed modularly and is easy to expand. NetFlow information collected from a true network device is taken as original data, and a simulation task file is formed after preprocessing, storage and traffic mapping are carried out on the original data. The simulation system reads the simulation task file for simulation. Each step from data collection to final simulation is taken into complete consideration. A method is provided for a large-scale data network to carry out schemes such as upgrade modification and network optimization. According to the method, the true traffic is approximated, and the data quantity cost is taken into consideration.