On the basis of the 24hour observation in Xi'an from 1996 to 2005, the daily atmospheric stability and ABL (atmospheric boundary layer) thickness are calculated by using the method of correctional Pasquill and according to the national standard GB/T 384091. The distribution characteristics of stability and ABL thickness are analyzed month by month and year by year, respectively. The re sults shows that the wind is the important factor to determine the atmospheric stabilities and ABL thickness.