Based on the reanalysis data of NCEP,some average fields from 30 thunderstorm days in Beijing area in summer from 2000 to 2005,such as CAPE,CIN,PWAT,ω,RH and LI,are analyzed to make out characteristics of large-scale environment fields of thunderstorm days.The results show that the CAPE has a rapid increasing process before thunderstorm occurrs,on the other hand,the CIN decreases gradually.The ω profile also shows that ascent activity occurs in the lower troposphere,while cold air and descent flow in the middle-upper troposphere are beneficial to the enhancement of instability layer.Stronger ascent velocity can touch the tropopause,higher RH area exists on the 600hPa,PWAT reaches its maximum,but LI is the minimum when thunderstorm takes place.By comparing average fields of 46 general storms with that of non-thunderstorms during May to August from 2004 to 2005,PWAT can be used to distinguish between the thunderstorm and general storm.The successful thunderstorm nowcasting could be achieved by analyzing Doppler weather radar reflectivity and radial velocity products.