In the summer of 1982,the first atmospheric science investigation had been performed in Xian, using an aircraft installed with PMS instruments. The case analysis of aerosol particles observation under fine weather condition is presented in this paper based on the data of 8. June The results show that the concentration of aerosol particles (0.5-8°m diameter) ranges from 4×10⁰-3.8×10¹/cm³, decreases with inereasing height.The temperature inversion layer has obstructive effect on the vertical transportation of aerosol particles. The particle size distribution expression and its parameters are given.