Abstract: The constant level balloons used to the authors were rubber balloons enclosed in silk envelopes of about 200 cm in diameter. Various properties of such a kind of constant level balloons were studied. Experimental results in the laboratory and upper air sounding data show that they are suitable for the purpose of studying clear air turbulence in the lower and middle txopos were. Five flights in the year of 1957-1958 were analysed. It seems that there exists pronounced gravity wave in deep layer of air over Peking when Pekiag is in the lee ward side of Yan Mountain range, i.e. the general air current is from around West-Northwest. There axe also some evidences for a vertical motion's periodicity of period longer than two hours.