Ground lightning flash density Ng is one of most important parameters in lightning risk assessment. The conventional method of lightning risk assessment is to adopt the observed annualmean number of thunder days (Td) from local meteorological stations to calculate Ng and consider it a constant for one city or even a certain area, which is of certain limitations as the distribution of lightning is depended on the topographical, geological, edaphic, meteorological, and environmental features. Based on the conception of Ng, the processed data from the calibrated lightning location system and the calculated Td by Kriging interpolation, a corresponding program is developed by the C# language to obtain more reliable values of Ng in a more convenient way for the use of lightning risk assessment.