An electrostatic probe is utilized to determine the ion distribution in a laminar flame. The probe is developed to be implemented in the ion measurement of combustion process contained in a solid container, and therefore the probe fabrication and the construction of a whole measurement system are explained in detail. Also, a numerical analysis is conducted to compare experimental measurement with the computed temperature and concentration. The ion distribution of four different flames of various fuel/air ratios is measured to analyze the distribution for understanding the combustion process. An explicit method is implemented to solve a set of partial differential equations of material and energy balances. Comparison between the measured distribution and the computed distribution of temperature indicates that the ion formation is closely related to the temperature distribution.