By means of the software programming and statistic methods, the data collected by three SAFIR3000 thunderstorm sensors are studied. Some useful conclusions about the distribution regularities of cloudtoground flushes in the Shanghai area are obtained: (1) because of the topography and high buildings in Shanghai, there occur more frequently lightning flushes in the north and south parts than in east and west parts, more frequently in the urban areas than in the rural areas; (2) although there are less flushes in the rural areas, the current is more powerful than that in the urban areas; (3) cloudtoground flushes happen mostly from 14:00 to 21:00. The number of lightning days is an important parameter that can be used to express the frequency of local lightning activity, but there are some problems in the use of this parameter in lightningprotection grade estimation and risk assessment. A suggestion to replace the number of lightning days with lightning density is presented and discussed.