Dynamic mold temperature (DMT) injection molding is a molding process that the mold cavity is first rapidly heated to a high temperature before plastic melt injection, and then cooled quickly after filling and packing stages. With this technique, plastic parts with very good surface performance can be produced. However, as the special mold structure and its worse working process, large stress concentration can be caused in the mold. Consequently, the mold for this new injection technology can be easily fatigue and the lifetime of the mold is inevitably decreased. In this paper, the structure of the mold was presented first, and then the working process and factors influencing the lifetime of the mold were analyzed. Through numerical simulation, the fatigue source of the mold was evaluated. Results showed that the evaluation process presented in this paper was very in accordance with the practical failure mold.