The number of thunderstorm days is an important parameter for studying the regularities of lightning activities. According to the mathematical and statistic analysis of thunderstorm data based on the manual observation from 1951 to 2009 and the measurements from the lightning location system from 1999 to 2008， an anaysis is made of the characteristics of the number of thunderstorm days and the ground flash density. It is concluded that the number of thunderstorm days from manual observation is much less than that measured by the lightning location system; both manual observation and lightning location system have some limitations： they cannot reflect objectively the regularities of lightning activities in different regions because of the methodology and sensitivity of the sounding devices. The effective thunderstorm parameters in various regions in Chongqing are obtained， which provides an academic basis for the evaluation of lightning disaster risk assessment and lightning protection design.