Based on the molecular dynamics simulation method, the evolution of Ag nanorods structure during the Ag nanorods relaxation process at various temperatures and lengths are intensively studied. The results show that there is a critical breaking temperature, which is decreasing with the increasing Ag naorods length. The Ag nanorod is melted to a highly disordered spherical cluster when the temperature is between the melting point and the critical breaking temperature. However, the Ag nanorod is melted to two spherical clusters when the temperature is above the critical breaking temperature.The physical mechanics of the structure evolution processe at various temperatures are presented.