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Based on the data of Doppler weather radars, automatic weather stations, radiosondes and satellites, the characteristics of clear air echoes in terms of reflectivity are analyzed using weather radar reflectivity factor and meteorological elements. The results show that the clear air echoes in different regions of China (North China, Central China, East China and South China) have obvious diurnal and annual variations. The specific performance is that the weather radar in the spring and autumn can detect obvious clear air echoes, which mainly appear between the evening and the following day. Further analysis shows that the clear air echoes detected by radars are closely related to the refractive index fluctuation. In addition, the presence of the inversion layer and the high-humidity region also has a high correlation with clear air echoes detected by weather radars.