This paper aims at designing a queueing model for clinics to reduce the waiting time for patients and increase the working efficiency for physicians. The current queueing model may cause time conflicts between patients with and without appointments especially when whom with the appointment comes late. Many hospitals tolerate the latecomers that may elicit dissatisfaction of other patients. In this research, we developed a new queueing model applying the strategy of dynamic punishment by moving back a certain percentage length of the existing queue for latecomers with appointments. Comparison of our new model with three existing ones demonstrated that ours is superior to others especially when handling the full load situation. The standard deviation of the new model is around 10% less than the other three models, indicating that fewer patients will fall into long-time waiting zone. In sum, our new model displays a better performance in case of full load situation by reducing the number of long-waiting-time patients and making the differences among waiting times smaller.