Experiments concerning a fast flame have been performed by many researchers, but it is impossible to observe some phenomena in the experimental frames only. The aim of this study is to show the numerical analysis of the fast flame that leads to deflagration-to-detonation transition (DDT). It was found that flame propagates with a supersonic velocity for some time before it transits to detonation. Additionally a new flame is developed in the vicinity of the wall due to compression shocks heating up the mixture along with adiabatic wall conditions. Moreover, on the tip of each flame one can observe a dense high-pressure and high-temperature region that forms a small but strong bow shock. This shock may be partly a clue in flame acceleration and DDT.