Identifying how pain transitions from acute to chronic is critical in designing effective prevention and management techniques. So it is necessary to find a way for a quantitative and predictive method to evaluate how pain trajectories are classified and then how we can effectively intervene them. In this paper,we use HPA model to simulate the pain trajectories. The cortisollevel values were classified into two different groups,and they present highstate and lowstate patterns. The highercortisol level was used to model the highintensity pain,and the lowerlevel to represent the lowpain or nopain. The results show the feasibility and the potential of developing such a broader model for patient evaluations.