Hydrothermal flame is a promising solution for problems in the preheating process of supercritical water oxidation (SCWO) technology. A detailed chemical kinetics coupled with a simple flow model is developed and validated to reflect the characteristic of hydrothermal flame. Analysis of free radicals accumulation show that the high quantity of free radicals induced by high methanol concentration leads to ignition. A method to approach the ignition temperature through ignition delay time calculation with a specific reactor model is proposed, which shows good agreement with the existing experimental data and directs further design quantitatively. Extinction limits are discussed by laminar flame speed and the perfect stirred reactor (PSR) model comparatively. Ultimate extinction temperatures of different methanol concentrations are approached and suggest the possible improvement of hydrothermal flame stability at higher methanol concentration through flow field optimization.