Clear air echo (CAE) helps to understand the structure of wind, temperature and humidity of the atmosphere; dualpolarization Doppler weather radar provides a wealth of information in detecting atmosphere. In this paper, CAE of Nanjing University of Information Science and Techonogy, CPol dualpolarization radar in summer of 2015 is taken as cases to analyze the wind, temperature and humidity structure of atmosphere and the impact factors of CAE, combined with the sounding observations. The characteristics of radar reflectivity factor Z, radial velocity Vr and differential reflectivity factor ZDR of CAE are analyzed. The results show that the uneven distribution of refractive index caused by the temperature, pressure and humidity gradients and the turbulence enhancement induced by the background wind field can cause the clear sky echo. The echo mechanism is turbulent scattering. The differential reflectivity factor is affected by the Doppler effect. The ZDR of CAE has different characteristics in different wind and air turbulence situations. The results are helpful for better understanding the impact of atmospheric wind, temperature and humidity structure on radar electromagnetic scattering and the quality control of radar data.