Abstract: In this paper, the intrinsic relationships between ignition delay times and the detonation cell size are analyzed, simulated from two one-step chemical kinetic models and one detailed chemical kinetic model. Ignition delay time for mixtures of hydrogen and air at 0.1MPa and 1.01MPa over the temperature range 800K to 1500K is investigated. The results demonstrate that the ignition delay time for one-step chemical kinetic model is independent of pressure, and linearly correlated with the initial temperature. The ignition delay time for the detailed chemical kinetic model is dependent of pressure, and is not linearly correlated with the initial temperature. However, in the inflection zone and the low temperature zone, the CFD results are 3 orders of magnitude smaller than the theoretical values. The CFD values of the ignition delay time differ from the theoretical ones by a factor as large as 10³. The detonation cell size simulated by all the chemical models is smaller than the experimental results, and the ignition delay time is proportional to the cell size. The detonation simulation results show that the longer the ignition delay time, the bigger the detonation cell size. The period of triple-point is almost equal to the ignition delay time of the gas behind the incident shock wave. Ignition delay time is a key parameter in detonation initiation and propagation.