Network-on-chip congestion greatly limits the effective performance of the router, and directly affects the performance of the processor chip. This paper divided the network's congestion state by using different threshold, and set the congestion avoidance apart into two distinct phases: congestion prevention and congestion relieving. Then a dynamic injection strategy was proposed. According to the congestion state in real-time, packet injection rate was adjusted dynamically, and communication traffic was controlled in reasonable level to decrease load press, avoiding congestion effectively. The simulation result shows that the performance of congestion prevention is almost at "Cliff" point, while congestion relieving is almost at "Knee" point, the injection rate can reach 0.05, and network performance is tradeoff with congestion avoidance.