Based on symmetric two-lane Nagel-Schreckenberg (STNS) model, a cellular automaton model of variable speed limit section in freeway is established with access to real-time traffic information of intelligent transportation system (ITS). The effects are discussed about how the different speed limit values, the lengths of speed limit section, and the different traffic states affect the traffic flow and the traffic volume via the simulation experiment of dynamic speed control. The effectual condition of speed limit is analyzed. The results of the examples show that speed limit can be used solely under some traffic states as an assistant traffic management strategy. The traffic jam phenomena can be suppressed and the goal of achieving a largest traffic flow and reducing the passing time of vehicles can be realized by using the dynamic speed control method with the different speed limit values and lengths under some traffic states.