Abstract: The essence of Sonic-Boom-Cloud is the water vapour condensation cloud caused by the local acceleration and the temperature decreased to the dew point and below, as the flying aircraft passes the high humidity air. It is more appropriate to call it the Condensation Cloud instead of the Sonic-Boom-Cloud. According to the flight speed and their different features, the Condensation Clouds can be divided into three types: the Low Subsonic Speed Irregular Condensation Cloud, the High Subsonic Speed Cone Condensation Cloud and the Supersonic Speed Cone Condensation Cloud. The formation mechanisms of the three types of Condensation Clouds, their different features, their relationship with the shock wave and the Sonic-Boom are discussed in this paper. The first type has no relationship with the Sonic-Boom. The second type is accompanied by the local weak shock wave, it does not break through the Sound Barrier and it is basically irrelevant with the Sonic Boom. The third type is related with the supersonic shock wave and the Sonic Boom.