By using aircraft sounding data (1949—1985) of 83 typhoons, the evolution of the double-ring cloud wall of concentric eye typhoons are analysed. It is found that there are three types of evolution: ① In the first type, accompanying the increase of typhoon intensity with time, the diameter of cloud wall encircled the original eye region of typhoon gradually shrinks. Meanwhile, a new cloud wall occur in the periphery of the region and then invade inward. So a double-ring cloud wall is formed. Then the inner wall rapidly disappears and the outer wall gradually shrinks. Usually, several processes similar to the above evolution may occur successively and the intensity of typhoon would oscillate with time. ② In the second type, a closed cloud wall occurs and invades from the periphery of the typhoon eye region. The evolution of the outer cloud wall is quite complex. It may sometimes shrink, and sometimes extend. In some cases the double-ring cloud wall lasts for a period of time, and in other cases its outer wall disappears rapidly. ③ In the third type, the double-ring cloud wall is formed as a result of the development of cumulus convection inner region of typhoon into a well-closed inner cloud wall. The inner wall usually lasts for a period of time and then rapidly disappears.
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