U-turn movement is a common form of traffic organization in urban streets. A traffic flow model for U-turn movement based on the NaSch cellular automaton model is proposed to simulate and analyze the dynamics of U-turn movement. The results indicated that the U-turn movement has significant effect on the traffic flow, and it is a typical bottleneck. The U-turn movement can cause phase transition at small probability of vehicle generation and the critical flow also decreases obviously. The system with two U-turn movement is different from the system with one U-turn movement in traffic features such as phase transition and critical flux. The one U-turn system has a good performance. It is suggested that the system with a couple of U-turns may help mitigate the negative effect of U-turn movement in traffic planning and management.