To balance the simulation time and accuracy, we proposed a dielectric breakdown simulator based on Monte Carlo stochastic method and the thermochemical molecular model. The simulator can self-consistently simulate the microscopic process of the time-dependent dielectric breakdown (TDDB). The evolution of the oxygen vacancies and potential distribution in the dielectric can be calculated. In addition, by verifying the reproduced the TDDB distribution with the experiment data, the simulator is proved to be able to predict the accurate device lifetime, thus enabling the reliability-aware design of gate stacks in future technology nodes.