Characteristic chemical time scale analysis plays a key role in the understanding of turbulence-chemistry interaction in turbulent combustion research and is also an important basis for the selection or development of combustion models in turbulent combustion modeling. A new method named main direction identification (MDID) was developed based on the modification of the CTS-ID (chemical time scale identification) method to achieve the function of identifying the characteristic time scale. Direction weight factor combined with mole fraction limit were used as a criterion in MDID to determine the characteristic time scale. MDID was applied to study characteristic chemical time scales of a CH4-O-2 inverse diffusion flame in hot syngas coflow, which is a model flame developed before to study the combustion process in partial oxidation reformers. Results show that the chemical time scale given by the MDID method is about 10(-5) s in the combustion area and 10(-2) s in the reforming area. The main reaction pathway was also analyzed using the MDID method. The new method was compared with three existing methods published in previous studies; the Damkohler numbers given by MDID are more consistent with the mild combustion nature of the flame compared with other methods. Then the MDID method was evaluated on a conventional oxy-fuel-type high temperature flame to assess its, flexibility to different reaction regimes. The time scale variation accurately reflects the changes of reaction regimes, indicating that the MDID method performs well on reacting flows varying from fast reaction regime to slow reaction regime. The effect of mole fraction limit on this method was also studied.