To meet the needs of failure reappearance of a certain rocket launching, the present research studied the conceivable failure condition by the method of numerical simulation. Firstly, the conceivable failure reasons were analyzed based on the failure phenomenon and the measure data from rocket. Then, the processes of the atomization and the combustion were numerically modeled and simulated, which was based on the performance of the gas generator. Next, the possible failure conditions were simulated one by one, and the results were compared with the limited data from the rocket. The conclusions are as follows: the numerical model proposed can simulate the rocket launching failure very well; the gas generator involved has some design objection, and needs to be optimized in design; the askew turbulent flow annulus is the most possible failure of this rocket launching.