This paper discusses the general characteristics and the wave inducec properties of air flow over water waves. In concern with the general characteristics of air flow, we treat the deviation of air velocity from the log-profile law near water surface. The effect of the instability Reynolds stress caused by the critical layer and the influence of the undulation of water surface are examined.
　The result shows that these two effects are not sufficient to explain actual phenomena, and the influence of the instability Reynolds stress and the jet effect, which may be caused by the loose boundary condition realized by the disagreement of stream line of air flow with the actual water surface, is introduced. The accurate discussion is not yet possible, and the rough estimation shows the method promising.
　Wave induced properties of air flow are investigated in both casse of U=0 and U≠0. In the former case high order approximations of the perturbed air flow are examined, and some properties of perturbed flow near the so called 'critical point' are discussed. In the latter case approximates olutions are obtained by the method of M. J. Lighthill(1957). The emergence of the instability Reynolds stress is discussed using the characterisics of the phase jump of the perturbed flow at the critical point, and some additional properites are also examined. Finally it is shown that the effect on the development of water waves by the instability Reynolds stress introduced in this paper seems to match the observed data in laboratory and ocean.